Is my CF Card failing?

I recently took my 1D III to a car show and took some shots. But when i went back later to look at the shots it said it couldn't display some of them, but some would still show. Now when i got home i looked at the file size and they were only 32kb (the bad ones)

is this a sign of a bad CF card?

If you put a different CF card in it - does it do the same thing? It has a secondary SD card slot - maybe see if it is doing something similar to files written to that card?

possibly. It sounds as if the file header got smashed. You can try and format and see if it was a one time occurrence, but I wouldn't use that card for any important stuff for some time.