From time to time I get this display on my SB700 when it's in TTL mode. (It's attached to a D80). When this happens, the flash works in manual mode, but not TTL. Changing modes on the camera doesn't make this go away, but sometimes it does go back to TTL mode all by itself. Another interesting tidbit: when I push the flash mode button on the camera, the built-in flash pops up, as if it didn't know there was an external flash attached. It seems like it never happens on fresh batteries, but it doesn't happen very often, so that might just be a coincidence.
There's no information on this in the manual. Any clues as to what's happening?