MSCRM Async Service exception

Hi everybody,

I have in my Windows Application log the following error:

Host CRM01: A Microsoft Dynamics CRM Asynchronous Processing Service operation of type adc8d523-24f6-4107-9dba-85d98d8ca647 has failed
Organization ID: JobId: de221d53-830c-4ad0-8f80-fa58a02bc203 OrgId:adc8d523-24f6-4107-9dba-85d98d8ca647 JobType:50; ErrorMessage: ErrorAction:Rethrow Exception:Unhandled Exception: System.Collections.Generic.KeyNotFoundException: Der angegebene Schlüssel war nicht im Wörterbuch angegeben.
bei System.Collections.Generic.Dictionary`2.get_Item(TKey key)
bei Microsoft.Crm.Asynchronous.EmailConnector.MailboxDataAccess.UpdateOutgoingMailbox(Mailbox mailbox, IAsyncEvent asyncEvent)
bei Microsoft.Crm.Asynchronous.EmailConnector.OutgoingEmailProviderBase.UpdateMailboxes()
bei Microsoft.Crm.Asynchronous.EmailConnector.OutgoingEmailProviderBase.Acknowledge()
bei Microsoft.Crm.Asynchronous.EmailConnector.OutgoingActivityProviderBase`1.Run()
bei Microsoft.Crm.Asynchronous.EmailConnector.OutgoingActivityOperation.InternalExecute(ActivityAsyncEvent asyncEvent)
bei Microsoft.Crm.Asynchronous.AsyncEventExecutionManager`2.ExecuteHandler(IAsyncEventHandlerFactory handlerFactory)
bei Microsoft.Crm.Asynchronous.PoolHandler.ProcessAsyncEvent(IAsyncEventExecutionManager asyncEventExecutionManager)

Organization Unique Name: %4
Error code: %5
Error description: %6

Does anybody know, how to fix it?

Br,

DrVer