Can you paste the text of the message? Its too fuzzy to read. I think it says something about not being able to delete? I would start on the Bus tab and try to delete there(guessing this bogus path is mapped to an output). Any(every) session you have opened since this started may need the same treatment.
Alternately, move the message box close to the lower right corner and upload just that area(a smaller area should show up clearer here) as I'd like to be able to see the info on Monitor Path, Audition Path, etc.
Also, I can see that the message is referring to Hardware Setup so that is another place that needs to be viewed
It may also be worth changing the IO setup to NOT allow Session Overwrite. Beyond that(and assuming Hardware Setup looks correct), I would try to delete all paths and then create what you really want.
FWIW, I have never seen this ever before(so trashing prefs is also a good idea)
