I'm working heavily with query notifications in SQL Server 2005 and I'm now
getting the following exception:

System.Collections.Generic.KeyNotFoundException: The given key was not 
present in the dictionary.

This was working for quite a while and then it stopped.  At first, the 
exception was intermittent, but now it's permanent.  The exception is 
happening deep inside of a System.Data.dll in a class called 
SqlDependencyProcessDispatcher in a method defined as follows:

private bool Start(string connectionString, out string server, out 
DbConnectionPoolIdentity identity, out string user, out string database, ref 
string queueService, string appDomainKey, SqlDependencyPerAppDomainDispatcher 
dispatcher, out bool errorOccurred, out bool appDomainStart, bool useDefaults)

It looks like the method is checking a dictionary for particular key; then, 
if it's found, it retrieves the item from the dictionary.  Looking at 
Reflector it appears that this lookup may not be threadsafe.  It has a few 
code blocks inside structured like this:

 if (!this._sqlDependencyPerAppDomainDispatchers.ContainsKey(appDomainKey))
        {
            lock (this._sqlDependencyPerAppDomainDispatchers)
            {
                this._sqlDependencyPerAppDomainDispatchers[appDomainKey] = 
dispatcher;
            }
        }

These should probably be using 
sqlDependencyPerAppDomainDispatchers.TryGetValue instead or should move the 
lock to the outside of the if statement.

No one on the Internet seems to have ever encountered this.

Two partial stack traces appear below.  They're partial in that I've 
ommitted a 
long set of calls from our interal app framework that are orthogonal to the 
problem.

The NT user making these calls is a local administrator on the database 
server.  The calls work a lot of the time, but break and seemingly random 
moments.

We use a preconfigured SQL Server Service Broker Queue named 
QueryChangeMessages and a service called QueryChangeNotifications.

Please help.

One stack trace looks like this:

[KeyNotFoundException: The given key was not present in the dictionary.]
   SqlDependencyProcessDispatcher.Start(String connectionString, String 
queue, String appDomainKey, SqlDependencyPerAppDomainDispatcher dispatcher) +0
   System.Data.SqlClient.SqlDependency.Start(String connectionString, String 
queue, Boolean useDefaults) +672
   System.Data.SqlClient.SqlDependency.Start(String connectionString, String 
queue) +7
   
Nvidia.PolicyInjection.CallHandlers.SqlDependencyConnection.StartInternal() 
+103

[DataException: An error occurred while calling 
ConfigurationManagement.Start for connection string named 
ConfigurationManagement on SQL Server Service Broker Queue 
QueryNotificationQueue.]
....

Another stack trace looks like this:

Server stack trace: 
   at System.ThrowHelper.ThrowKeyNotFoundException()
   at System.Collections.Generic.Dictionary`2.get_Item(TKey key)
   at 
SqlDependencyProcessDispatcher.SqlConnectionContainer.ProcessNotificationResults(SqlDataReader reader)
   at 
SqlDependencyProcessDispatcher.SqlConnectionContainer.SynchronouslyQueryServiceBrokerQueue()
   at 
SqlDependencyProcessDispatcher.SqlConnectionContainer..ctor(SqlConnectionContainerHashHelper hashHelper, String appDomainKey, Boolean useDefaults)
   at SqlDependencyProcessDispatcher.Start(String connectionString, String& 
server, DbConnectionPoolIdentity& identity, String& user, String& database, 
String& queueService, String appDomainKey, 
SqlDependencyPerAppDomainDispatcher dispatcher, Boolean& errorOccurred, 
Boolean& appDomainStart, Boolean useDefaults)
   at SqlDependencyProcessDispatcher.Start(String connectionString, String 
queue, String appDomainKey, SqlDependencyPerAppDomainDispatcher dispatcher)
   at 
System.Runtime.Remoting.Messaging.StackBuilderSink._PrivateProcessMessage(IntPtr 
md, Object[] args, Object server, Int32 methodPtr, Boolean fExecuteInContext, 
Object[]& outArgs)
   at 
System.Runtime.Remoting.Messaging.StackBuilderSink.PrivateProcessMessage(RuntimeMethodHandle 
md, Object[] args, Object server, Int32 methodPtr, Boolean fExecuteInContext, 
Object[]& outArgs)
   at 
System.Runtime.Remoting.Messaging.StackBuilderSink.SyncProcessMessage(IMessage msg, Int32 methodPtr, Boolean fExecuteInContext)

Exception rethrown at [0]: 
   at System.Runtime.Remoting.Proxies.RealProxy.HandleReturnMessage(IMessage 
reqMsg, IMessage retMsg)
   at System.Runtime.Remoting.Proxies.RealProxy.PrivateInvoke(MessageData& 
msgData, Int32 type)
   at SqlDependencyProcessDispatcher.Start(String connectionString, String 
queue, String appDomainKey, SqlDependencyPerAppDomainDispatcher dispatcher)
   at System.Data.SqlClient.SqlDependency.Start(String connectionString, 
String queue, Boolean useDefaults)
   at System.Data.SqlClient.SqlDependency.Start(String connectionString, 
String queue)
....