I'm sorry I can only imagine how frustrating this is. This might be a computer problem.
As I mentioned earlier, it's possible for a segiment of a hard drive to go bad and corrupt data. If that happened and the data was in the sectioin that stored the program for interperting the RAW, you might experience behaivor like your seeing. There is a report on Aperture Expert where images on a remote drive became "unsupported format" after being moved to a remote drive. The problem turned out to be a bad firewire cable.
Once more just to be sure my system info: