diff --git a/xpcom/base/nsError.h b/xpcom/base/nsError.h
index 0f1c791d1e5..e430b264951 100644
--- a/xpcom/base/nsError.h
+++ b/xpcom/base/nsError.h
@@ -176,6 +176,20 @@ typedef PRUint32 nsresult;
 /* Returned when a factory already is registered */
 #define NS_ERROR_FACTORY_EXISTS            (NS_ERROR_BASE + 0x100)
 
+
+/* Returned when a proxy could not be create a proxy for one of the IN parameters
+   This is returned only when the "real" meathod has NOT been invoked. 
+*/
+
+#define NS_ERROR_PROXY_INVALID_IN_PARAMETER        ((nsresult) 0x80010010L)
+
+/* Returned when a proxy could not be create a proxy for one of the OUT parameters
+   This is returned only when the "real" meathod has ALREADY been invoked. 
+*/
+
+#define NS_ERROR_PROXY_INVALID_OUT_PARAMETER        ((nsresult) 0x80010011L)
+
+
 /*@}*/
 
 ////////////////////////////////////////////////////////////////////////////////
diff --git a/xpcom/proxy/public/nsProxyEvent.h b/xpcom/proxy/public/nsProxyEvent.h
index 75f1ae5fcf2..72668f0dbf9 100644
--- a/xpcom/proxy/public/nsProxyEvent.h
+++ b/xpcom/proxy/public/nsProxyEvent.h
@@ -95,7 +95,7 @@ class nsProxyObject : public nsISupports
 
         } AutoProxyConvertTypes;
         
-        void                AutoProxyParameterList(nsXPTMethodInfo *methodInfo, nsXPTCMiniVariant * params, 
+        nsresult            AutoProxyParameterList(nsXPTMethodInfo *methodInfo, nsXPTCMiniVariant * params, 
                                                    nsIInterfaceInfo *interfaceInfo, AutoProxyConvertTypes convertType);
 
         nsIEventQueue       *mDestQueue;                 /* destination queue */
diff --git a/xpcom/proxy/src/nsProxyEvent.cpp b/xpcom/proxy/src/nsProxyEvent.cpp
index 991f4186cc2..07518664c19 100644
--- a/xpcom/proxy/src/nsProxyEvent.cpp
+++ b/xpcom/proxy/src/nsProxyEvent.cpp
@@ -144,9 +144,11 @@ nsProxyObject::Post( PRUint32 methodIndex, nsXPTMethodInfo *methodInfo, nsXPTCMi
     ///////////////////////////////////////////////////////////////////////
     // Auto-proxification
     ///////////////////////////////////////////////////////////////////////
-    AutoProxyParameterList(methodInfo, params, interfaceInfo, convertInParameters);
+    nsresult rv = AutoProxyParameterList(methodInfo, params, interfaceInfo, convertInParameters);
     ///////////////////////////////////////////////////////////////////////
-
+    
+    if (NS_FAILED(rv))
+        return rv;
 
     // convert the nsXPTCMiniVariant to a nsXPTCVariant
 
@@ -187,13 +189,13 @@ nsProxyObject::Post( PRUint32 methodIndex, nsXPTMethodInfo *methodInfo, nsXPTCMi
     {
         mDestQueue->PostSynchronousEvent(event, nsnull);
         
-        nsresult rv = proxyInfo->GetResult();
+        rv = proxyInfo->GetResult();
         delete proxyInfo;
 
         ///////////////////////////////////////////////////////////////////////
         // Auto-proxification
         ///////////////////////////////////////////////////////////////////////
-        AutoProxyParameterList(methodInfo, params, interfaceInfo, convertOutParameters);
+        rv = AutoProxyParameterList(methodInfo, params, interfaceInfo, convertOutParameters);
         ///////////////////////////////////////////////////////////////////////
         
         mDestQueue->ExitMonitor();
@@ -212,7 +214,7 @@ nsProxyObject::Post( PRUint32 methodIndex, nsXPTMethodInfo *methodInfo, nsXPTCMi
 }
 
 
-void
+nsresult
 nsProxyObject::AutoProxyParameterList(nsXPTMethodInfo *methodInfo, nsXPTCMiniVariant * params, 
                                       nsIInterfaceInfo *interfaceInfo, AutoProxyConvertTypes convertType)
 {
@@ -262,20 +264,27 @@ nsProxyObject::AutoProxyParameterList(nsXPTMethodInfo *methodInfo, nsXPTCMiniVar
 
                     interfaceInfo->GetIIDForParam(&paramInfo, &iid);
 
-                    manager->GetProxyObject( GetQueue(), 
-                                             *iid,
-                                             anInterface, 
-                                             GetProxyType(), 
-                                             (void**) &aProxyObject);
+                    rv = manager->GetProxyObject(GetQueue(), 
+                                                 *iid,
+                                                 anInterface, 
+                                                 GetProxyType(), 
+                                                 (void**) &aProxyObject);
 
                     nsAllocator::Free((void*)iid);
-                    
+                    NS_RELEASE(manager);
+
+                    if (NS_FAILED(rv))
+                        return rv;
+
                     if (paramInfo.IsOut())
                         *((void**)params[i].val.p) = ((void*)aProxyObject);
                     else
                         (params[i].val.p)  = ((void*)aProxyObject);                    
-
-                    NS_RELEASE(manager);
+                }
+                else
+                {   
+                    // Could not get nsIProxyObjectManager
+                    return rv;
                 }
             } 
             else