Bingo! TommyK nailed it. I depressed the spring contacts that would run underneath the accessory flash and the camera stopped 'seeing' the phantom flash. The problem occurred after removing a 430EX, so there's a match as well.
Ordo, the "Flash Control" menu takes me to the internal and external settings. Before I 'fixed' the camera the internal flash settings displayed an error message indicating an external flash was connected. The external flash menu indicated an external flash was present but not recognized.