>>I think the above just implies that a method in the service threw an exception. There's probably more info in the InnerException if you can get it.
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>I cannot access the InnerException as this one bypassed my error handler which explains why it falls into the Event Viewer. This is not reproducable. It happened once and once I restarted the service, it went ok and processed the same record it failed on previously. So, for now, it is still running in service mode but will fail again until I find what is in cause.
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>If it would have failed again when I restarted the service, I would have been able to trace more into it until I find the exact line which triggered it. But, as surprise as it got, just restarting the service made it processing that record ok.

What exception handling do you have in the method? - you should be able to catch it there before TargetInvocationException kicks in.

Also, since this is intermittent, is it possible that a previous call to the method had not completed before the timer fired again?
If that's a possiblility you will need to ensure that your code is re-entrant....