Hi Wolfgang,
Just for your WCF adapter scenario, you can go to the Transport Advanced Options tab on your Send port and check the “Enable routing for failed messages” checkbox to capture any failed messages that come back in the response from the call to the WCF adapter. You can then set up another Send port to filter on these failed messages from the WCF adapter and save them as files to the file system, and you can have a third-party file watcher program to notify you of any new files created in that folder.
Just a suggestion which does not involve any external logging component, and something more substantial than periodically checking the Event Viewer for any error messages logged by BizTalk engine.
Daniel.