diff --git a/gns3server/modules/dynamips/backends/atmsw.py b/gns3server/modules/dynamips/backends/atmsw.py
index 98469748..dc6ff30c 100644
--- a/gns3server/modules/dynamips/backends/atmsw.py
+++ b/gns3server/modules/dynamips/backends/atmsw.py
@@ -83,7 +83,11 @@ class ATMSW(object):
         #TODO: JSON schema validation for the request
         log.debug("received request {}".format(request))
         atmsw_id = request["id"]
+        if atmsw_id not in self._atm_switches:
+            self.send_custom_error("ATM switch id {} doesn't exist".format(atmsw_id))
+            return
         atmsw = self._atm_switches[atmsw_id]
+
         try:
             atmsw.delete()
             self._hypervisor_manager.unallocate_hypervisor_for_simulated_device(atmsw)
@@ -117,6 +121,9 @@ class ATMSW(object):
         #TODO: JSON schema validation for the request
         log.debug("received request {}".format(request))
         atmsw_id = request["id"]
+        if atmsw_id not in self._atm_switches:
+            self.send_custom_error("ATM switch id {} doesn't exist".format(atmsw_id))
+            return
         atmsw = self._atm_switches[atmsw_id]
 
         # rename the switch if requested
@@ -153,6 +160,9 @@ class ATMSW(object):
         #TODO: JSON schema validation for the request
         log.debug("received request {}".format(request))
         atmsw_id = request["id"]
+        if atmsw_id not in self._atm_switches:
+            self.send_custom_error("ATM switch id {} doesn't exist".format(atmsw_id))
+            return
         atmsw = self._atm_switches[atmsw_id]
 
         try:
@@ -207,6 +217,9 @@ class ATMSW(object):
         #TODO: JSON schema validation for the request
         log.debug("received request {}".format(request))
         atmsw_id = request["id"]
+        if atmsw_id not in self._atm_switches:
+            self.send_custom_error("ATM switch id {} doesn't exist".format(atmsw_id))
+            return
         atmsw = self._atm_switches[atmsw_id]
 
         port = request["port"]
@@ -273,6 +286,9 @@ class ATMSW(object):
         #TODO: JSON schema validation for the request
         log.debug("received request {}".format(request))
         atmsw_id = request["id"]
+        if atmsw_id not in self._atm_switches:
+            self.send_custom_error("ATM switch id {} doesn't exist".format(atmsw_id))
+            return
         atmsw = self._atm_switches[atmsw_id]
         port = request["port"]
 
diff --git a/gns3server/modules/dynamips/backends/ethhub.py b/gns3server/modules/dynamips/backends/ethhub.py
index 60c5d959..68e9852f 100644
--- a/gns3server/modules/dynamips/backends/ethhub.py
+++ b/gns3server/modules/dynamips/backends/ethhub.py
@@ -82,7 +82,11 @@ class ETHHUB(object):
         #TODO: JSON schema validation for the request
         log.debug("received request {}".format(request))
         ethhub_id = request["id"]
+        if ethhub_id not in self._ethernet_hubs:
+            self.send_custom_error("Ethernet hub id {} doesn't exist".format(ethhub_id))
+            return
         ethhub = self._ethernet_hubs[ethhub_id]
+
         try:
             ethhub.delete()
             self._hypervisor_manager.unallocate_hypervisor_for_simulated_device(ethhub)
@@ -116,6 +120,9 @@ class ETHHUB(object):
         #TODO: JSON schema validation for the request
         log.debug("received request {}".format(request))
         ethhub_id = request["id"]
+        if ethhub_id not in self._ethernet_hubs:
+            self.send_custom_error("Ethernet hub id {} doesn't exist".format(ethhub_id))
+            return
         ethhub = self._ethernet_hubs[ethhub_id]
 
         # rename the hub if requested
@@ -152,6 +159,9 @@ class ETHHUB(object):
         #TODO: JSON schema validation for the request
         log.debug("received request {}".format(request))
         ethhub_id = request["id"]
+        if ethhub_id not in self._ethernet_hubs:
+            self.send_custom_error("Ethernet hub id {} doesn't exist".format(ethhub_id))
+            return
         ethhub = self._ethernet_hubs[ethhub_id]
 
         try:
@@ -205,6 +215,9 @@ class ETHHUB(object):
         #TODO: JSON schema validation for the request
         log.debug("received request {}".format(request))
         ethhub_id = request["id"]
+        if ethhub_id not in self._ethernet_hubs:
+            self.send_custom_error("Ethernet hub id {} doesn't exist".format(ethhub_id))
+            return
         ethhub = self._ethernet_hubs[ethhub_id]
         port = request["port"]
 
@@ -247,6 +260,9 @@ class ETHHUB(object):
         #TODO: JSON schema validation for the request
         log.debug("received request {}".format(request))
         ethhub_id = request["id"]
+        if ethhub_id not in self._ethernet_hubs:
+            self.send_custom_error("Ethernet hub id {} doesn't exist".format(ethhub_id))
+            return
         ethhub = self._ethernet_hubs[ethhub_id]
         port = request["port"]
 
diff --git a/gns3server/modules/dynamips/backends/ethsw.py b/gns3server/modules/dynamips/backends/ethsw.py
index 430b4010..316258ad 100644
--- a/gns3server/modules/dynamips/backends/ethsw.py
+++ b/gns3server/modules/dynamips/backends/ethsw.py
@@ -82,7 +82,11 @@ class ETHSW(object):
         #TODO: JSON schema validation for the request
         log.debug("received request {}".format(request))
         ethsw_id = request["id"]
+        if ethsw_id not in self._ethernet_switches:
+            self.send_custom_error("Ethernet switch id {} doesn't exist".format(ethsw_id))
+            return
         ethsw = self._ethernet_switches[ethsw_id]
+
         try:
             ethsw.delete()
             self._hypervisor_manager.unallocate_hypervisor_for_simulated_device(ethsw)
@@ -117,6 +121,9 @@ class ETHSW(object):
         #TODO: JSON schema validation for the request
         log.debug("received request {}".format(request))
         ethsw_id = request["id"]
+        if ethsw_id not in self._ethernet_switches:
+            self.send_custom_error("Ethernet switch id {} doesn't exist".format(ethsw_id))
+            return
         ethsw = self._ethernet_switches[ethsw_id]
 
         if "ports" in request:
@@ -171,6 +178,9 @@ class ETHSW(object):
         #TODO: JSON schema validation for the request
         log.debug("received request {}".format(request))
         ethsw_id = request["id"]
+        if ethsw_id not in self._ethernet_switches:
+            self.send_custom_error("Ethernet switch id {} doesn't exist".format(ethsw_id))
+            return
         ethsw = self._ethernet_switches[ethsw_id]
 
         try:
@@ -226,6 +236,9 @@ class ETHSW(object):
         #TODO: JSON schema validation for the request
         log.debug("received request {}".format(request))
         ethsw_id = request["id"]
+        if ethsw_id not in self._ethernet_switches:
+            self.send_custom_error("Ethernet switch id {} doesn't exist".format(ethsw_id))
+            return
         ethsw = self._ethernet_switches[ethsw_id]
 
         port = request["port"]
@@ -276,6 +289,9 @@ class ETHSW(object):
         #TODO: JSON schema validation for the request
         log.debug("received request {}".format(request))
         ethsw_id = request["id"]
+        if ethsw_id not in self._ethernet_switches:
+            self.send_custom_error("Ethernet switch id {} doesn't exist".format(ethsw_id))
+            return
         ethsw = self._ethernet_switches[ethsw_id]
         port = request["port"]
 
diff --git a/gns3server/modules/dynamips/backends/frsw.py b/gns3server/modules/dynamips/backends/frsw.py
index 1460e095..3432d47e 100644
--- a/gns3server/modules/dynamips/backends/frsw.py
+++ b/gns3server/modules/dynamips/backends/frsw.py
@@ -82,7 +82,11 @@ class FRSW(object):
         #TODO: JSON schema validation for the request
         log.debug("received request {}".format(request))
         frsw_id = request["id"]
+        if frsw_id not in self._frame_relay_switches:
+            self.send_custom_error("Frame relay switch id {} doesn't exist".format(frsw_id))
+            return
         frsw = self._frame_relay_switches[frsw_id]
+
         try:
             frsw.delete()
             self._hypervisor_manager.unallocate_hypervisor_for_simulated_device(frsw)
@@ -116,6 +120,9 @@ class FRSW(object):
         #TODO: JSON schema validation for the request
         log.debug("received request {}".format(request))
         frsw_id = request["id"]
+        if frsw_id not in self._frame_relay_switches:
+            self.send_custom_error("Frame relay switch id {} doesn't exist".format(frsw_id))
+            return
         frsw = self._frame_relay_switches[frsw_id]
 
         # rename the switch if requested
@@ -151,6 +158,9 @@ class FRSW(object):
         #TODO: JSON schema validation for the request
         log.debug("received request {}".format(request))
         frsw_id = request["id"]
+        if frsw_id not in self._frame_relay_switches:
+            self.send_custom_error("Frame relay switch id {} doesn't exist".format(frsw_id))
+            return
         frsw = self._frame_relay_switches[frsw_id]
 
         try:
@@ -205,6 +215,9 @@ class FRSW(object):
         #TODO: JSON schema validation for the request
         log.debug("received request {}".format(request))
         frsw_id = request["id"]
+        if frsw_id not in self._frame_relay_switches:
+            self.send_custom_error("Frame relay switch id {} doesn't exist".format(frsw_id))
+            return
         frsw = self._frame_relay_switches[frsw_id]
 
         port = request["port"]
@@ -258,6 +271,9 @@ class FRSW(object):
         #TODO: JSON schema validation for the request
         log.debug("received request {}".format(request))
         frsw_id = request["id"]
+        if frsw_id not in self._frame_relay_switches:
+            self.send_custom_error("Frame relay switch id {} doesn't exist".format(frsw_id))
+            return
         frsw = self._frame_relay_switches[frsw_id]
         port = request["port"]
 
diff --git a/gns3server/modules/dynamips/backends/vm.py b/gns3server/modules/dynamips/backends/vm.py
index 84e581d2..9e21c8bb 100644
--- a/gns3server/modules/dynamips/backends/vm.py
+++ b/gns3server/modules/dynamips/backends/vm.py
@@ -209,7 +209,11 @@ class VM(object):
         #TODO: JSON schema validation for the request
         log.debug("received request {}".format(request))
         router_id = request["id"]
+        if router_id not in self._routers:
+            self.send_custom_error("IOS router id {} doesn't exist".format(router_id))
+            return
         router = self._routers[router_id]
+
         try:
             router.delete()
             self._hypervisor_manager.unallocate_hypervisor_for_router(router)
@@ -240,7 +244,11 @@ class VM(object):
         #TODO: JSON schema validation for the request
         log.debug("received request {}".format(request))
         router_id = request["id"]
+        if router_id not in self._routers:
+            self.send_custom_error("IOS router id {} doesn't exist".format(router_id))
+            return
         router = self._routers[router_id]
+
         try:
             router.start()
         except DynamipsError as e:
@@ -269,7 +277,11 @@ class VM(object):
         #TODO: JSON schema validation for the request
         log.debug("received request {}".format(request))
         router_id = request["id"]
+        if router_id not in self._routers:
+            self.send_custom_error("IOS router id {} doesn't exist".format(router_id))
+            return
         router = self._routers[router_id]
+
         try:
             router.stop()
         except DynamipsError as e:
@@ -298,7 +310,11 @@ class VM(object):
         #TODO: JSON schema validation for the request
         log.debug("received request {}".format(request))
         router_id = request["id"]
+        if router_id not in self._routers:
+            self.send_custom_error("IOS router id {} doesn't exist".format(router_id))
+            return
         router = self._routers[router_id]
+
         try:
             router.suspend()
         except DynamipsError as e:
@@ -327,6 +343,9 @@ class VM(object):
         #TODO: JSON schema validation for the request
         log.debug("received request {}".format(request))
         router_id = request["id"]
+        if router_id not in self._routers:
+            self.send_custom_error("IOS router id {} doesn't exist".format(router_id))
+            return
         router = self._routers[router_id]
         try:
             if router.get_status() != "inactive":
@@ -363,6 +382,9 @@ class VM(object):
         #TODO: JSON schema validation for the request
         log.debug("received request {}".format(request))
         router_id = request["id"]
+        if router_id not in self._routers:
+            self.send_custom_error("IOS router id {} doesn't exist".format(router_id))
+            return
         router = self._routers[router_id]
 
         try:
@@ -454,7 +476,11 @@ class VM(object):
         #TODO: JSON schema validation for the request
         log.debug("received request {}".format(request))
         router_id = request["id"]
+        if router_id not in self._routers:
+            self.send_custom_error("IOS router id {} doesn't exist".format(router_id))
+            return
         router = self._routers[router_id]
+
         try:
             if router.startup_config or router.private_config:
 
@@ -509,6 +535,9 @@ class VM(object):
         #TODO: JSON schema validation for the request
         log.debug("received request {}".format(request))
         router_id = request["id"]
+        if router_id not in self._routers:
+            self.send_custom_error("IOS router id {} doesn't exist".format(router_id))
+            return
         router = self._routers[router_id]
 
         try:
@@ -549,6 +578,9 @@ class VM(object):
         #TODO: JSON schema validation for the request
         log.debug("received request {}".format(request))
         router_id = request["id"]
+        if router_id not in self._routers:
+            self.send_custom_error("IOS router id {} doesn't exist".format(router_id))
+            return
         router = self._routers[router_id]
 
         try:
@@ -603,6 +635,9 @@ class VM(object):
         #TODO: JSON schema validation for the request
         log.debug("received request {}".format(request))
         router_id = request["id"]
+        if router_id not in self._routers:
+            self.send_custom_error("IOS router id {} doesn't exist".format(router_id))
+            return
         router = self._routers[router_id]
 
         slot = request["slot"]
@@ -649,6 +684,9 @@ class VM(object):
         log.debug("received request {}".format(request))
         router_id = request["id"]
         router = self._routers[router_id]
+        if router_id not in self._routers:
+            self.send_custom_error("IOS router id {} doesn't exist".format(router_id))
+            return
         slot = request["slot"]
         port = request["port"]
 
diff --git a/gns3server/modules/iou/__init__.py b/gns3server/modules/iou/__init__.py
index d98da3fe..af0198b1 100644
--- a/gns3server/modules/iou/__init__.py
+++ b/gns3server/modules/iou/__init__.py
@@ -291,7 +291,11 @@ class IOU(IModule):
         #TODO: JSON schema validation for the request
         log.debug("received request {}".format(request))
         iou_id = request["id"]
+        if iou_id not in self._iou_instances:
+            self.send_custom_error("IOU device id {} doesn't exist".format(iou_id))
+            return
         iou_instance = self._iou_instances[iou_id]
+
         try:
             iou_instance.delete()
             del self._iou_instances[iou_id]
@@ -325,6 +329,9 @@ class IOU(IModule):
         #TODO: JSON schema validation for the request
         log.debug("received request {}".format(request))
         iou_id = request["id"]
+        if iou_id not in self._iou_instances:
+            self.send_custom_error("IOU device id {} doesn't exist".format(iou_id))
+            return
         iou_instance = self._iou_instances[iou_id]
 
         try:
@@ -378,7 +385,11 @@ class IOU(IModule):
         #TODO: JSON schema validation for the request
         log.debug("received request {}".format(request))
         iou_id = request["id"]
+        if iou_id not in self._iou_instances:
+            self.send_custom_error("IOU device id {} doesn't exist".format(iou_id))
+            return
         iou_instance = self._iou_instances[iou_id]
+
         try:
             log.debug("starting IOU with command: {}".format(iou_instance.command()))
             iou_instance.iouyap = self._iouyap
@@ -410,7 +421,11 @@ class IOU(IModule):
         #TODO: JSON schema validation for the request
         log.debug("received request {}".format(request))
         iou_id = request["id"]
+        if iou_id not in self._iou_instances:
+            self.send_custom_error("IOU device id {} doesn't exist".format(iou_id))
+            return
         iou_instance = self._iou_instances[iou_id]
+
         try:
             iou_instance.stop()
         except IOUError as e:
@@ -439,7 +454,11 @@ class IOU(IModule):
         #TODO: JSON schema validation for the request
         log.debug("received request {}".format(request))
         iou_id = request["id"]
+        if iou_id not in self._iou_instances:
+            self.send_custom_error("IOU device id {} doesn't exist".format(iou_id))
+            return
         iou_instance = self._iou_instances[iou_id]
+
         try:
             if iou_instance.is_running():
                 iou_instance.stop()
@@ -472,6 +491,9 @@ class IOU(IModule):
         #TODO: JSON schema validation for the request
         log.debug("received request {}".format(request))
         iou_id = request["id"]
+        if iou_id not in self._iou_instances:
+            self.send_custom_error("IOU device id {} doesn't exist".format(iou_id))
+            return
         iou_instance = self._iou_instances[iou_id]
 
         try:
@@ -528,6 +550,9 @@ class IOU(IModule):
         #TODO: JSON schema validation for the request
         log.debug("received request {}".format(request))
         iou_id = request["id"]
+        if iou_id not in self._iou_instances:
+            self.send_custom_error("IOU device id {} doesn't exist".format(iou_id))
+            return
         iou_instance = self._iou_instances[iou_id]
 
         slot = request["slot"]
@@ -608,6 +633,9 @@ class IOU(IModule):
         log.debug("received request {}".format(request))
         iou_id = request["id"]
         iou_instance = self._iou_instances[iou_id]
+        if iou_id not in self._iou_instances:
+            self.send_custom_error("IOU device id {} doesn't exist".format(iou_id))
+            return
         slot = request["slot"]
         port = request["port"]
 
diff --git a/setup.py b/setup.py
index 1a953246..0bb95ed1 100644
--- a/setup.py
+++ b/setup.py
@@ -68,6 +68,7 @@ setup(
         "Programming Language :: Python",
         "Programming Language :: Python :: 3",
         "Programming Language :: Python :: 3.3",
+        "Programming Language :: Python :: 3.4",
         "Programming Language :: Python :: Implementation :: CPython",
         ],
 )
diff --git a/tox.ini b/tox.ini
index 84900ea9..b10796da 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,5 +1,5 @@
 [tox]
-envlist = py33
+envlist = py33, py34
 
 [testenv]
 commands = py.test [] -s tests