If you have itineraries which are using the Itinerary Service Broker, along with the XPath filter, you might run into a very strange looking error which will take you down all kinds of rabbit holes.

There was a failure executing the receive pipeline: “[fully qualified name of your pipeline]”
Source: “ESB Dispatcher” Receive Port: “[name of your receive port]” URI: “[port URI]”
Reason: The source was not found, but some or all event logs could not be searched.  Inaccessible logs: Security.

Reading this at face value, you naturally start looking into the permissions of the service account used by the BizTalk host instance linked to the receive location.  It turns out the error has nothing to do with the security log, but rather a bug in the ESB Toolkit’s deployment, where the XPath Filter dll has an extra “L” added to the file extension:

Bad XPath Filter DLL extensions

Just remove the extra “L” from the file and things will once again work!.