CF Problems on a 20D. Help please!
Probably your card, as you could see the images in the camera. Possibly so, even if it happened to two cards. Were the cards the same? From the same source? Stored submerged in the same tank of sulfurous acid? Get a replacement card - they're dirt cheap.
Anyhow, use a good card reader rather than connecting the camera.
I also still have my 6yr old 20D, still works, unfortunately
The problem with being at the cutting edge is that you tend to get sliced from time to time.