I ran into something similar last weekend...only this was really weird. I recorded the first set of a show going MME>SPDIF>VX>Wavelab 5.0 and had no problems. At the set break, I stopped the recording & saved the file. With no changes to settings on computer, programs, MME or even closing out Wavelab again, I hit the record. Normally, it just starts recording to a new file (I always use the auto split function in the record window). Got the error message that the card wasn't recognized. I didn't think much of it, as I figured it was just the VX's Windows driver going wonky again. So, I shut down and restart, remove & re-install the driver, come back into Wavelab only to get the same message. I tried Soundforge 6 also...no soap.
I swapped the SPDIF to my 'P1 and continued to work on the lappy while the second set started. Tried another install of the driver, going first to Soundforge and still no recognizing the digi in on the VX Pocket. I switch from Ian's creation (which has worked great from day one) to the full breakout cable and tried digi in there. Still no joy. Finally, I go analog-in using the XLR's on the breakout cable, switch the VX to analog and voila: signal. Recorded the rest of the show with no hitches.
I've had to do the driver reinstall a number of times before, but usually only at the initial startup. I just figured my lappy (always a thorn in my recording side) had finally gone around the bend. Seems as though something more sinister was going on. Wish I'd know that before I tossed the lappy against the wall.
The moral: always check the Tapersection first if you run into a technical problem.