Thanks everyone, I'm posting from the old 6400 right now. It would appear to be a bad DIMM as suggested. I had a 64, a 32 and the 8 soldered onto the board for a total of 104. I removed the 32 and replaced it with an old 8 I had laying around, reset the CUDA switch and here we are. This was after swapping DIMMs around, running without one and then the other, etc., etc.
Maybe now I'll shop for a cheap 64 someplace. This old dog is only a backup so I'm not dumping that much money into it.