when it is in the drive reader (not your camera)? If so, I'd try saving a pic from your computer to the drive, and see what happens... Have you been able to access other data (mp3s, Word docs, etc) on that card, in that reader?

It reminds me of an add-on reader I had on my computer (actually 2 of them); they never worked well, VERY buggy. When I got a new computer, I got an HP with a multi-card reader as standard equipment; of course it works flawlessly...