I don't know... The better bet is to get a cheap new card reader that supports SD/SDHC... There are lots of "issues" with various models of cameras (can't force format for FAT16, may not be able to make the card "bootable", can't always copy RAW images from camera, etc.).
Otherwise, just try another version(s) of CHDK for your camera. Won't hurt anything.
Lastly, the A620 is one of the few with a real firmware update from Canon:
FAQ - CHDK WikiThe "real" firmware update carries with it the chance of failing to correctly update your camera (Bricking your camera)--it would probably be a last resort (after you get a real card reader--or borrow one from a friend).
-Bill