Exception handler fault - I think this is something built into the phoenix ROMs, I don't think it's an original Capcom thing. If this game has been running fine for months it means one of your main program ROMs has died or is not working correctly. Normally this kind of fault occurs because the wrong region code has been installed.
Try opening up your B board and removing/reinstalling all of your ROMs and see if that helps. I seem to remember that the phoenix set replaces most of the original EPROMs on the board. 1 and 2 are the Q Sound ROMs so I don't think these get rewritten when using phoenix but I can't remember off the top of my head.
Either way, open up your B board and carefully remove and reinstall all of the EPROMs on your board (1-2 for Q Sound, I think it's 3-10 for main code) and see if the issue remains. If it does, do you have a programmer or access to one to dump your ROMs and see if any have failed?
Others who know more about how the exception handler works might be able to help more.