Canon Rebel XT: Error 99 and "busy"?

Question:

Canon Rebel XT: Error 99 and "busy"?

Anyone know what might be up with my camera?
Last Saturday, I was shooting a six band concert. During the third band, it refused to take any more pictures, and kept giving me an Error 99 message.
I took the lens off and cleaned it, took the battery out and cleaned off the contacts, and took the memory card out.
Nothing helped.
I downloaded my images to my computer just fine, but the camera was pretty much dead.
It stayed like that until Monday, when it mysteriously decided to start working again.
Or so I thought...

This evening I took it out and shot about two hundred pics just fine. The only problem I have is now I can't download my images! It keeps telling me that it's busy.

Anyone have any ideas? I'm going to take it to a camera store on Monday and talk to them, but I'm perplexed and wondering what this could be.
A memory card malfunction?

Best Answer - Chosen by Asker: An Error 99 signifies that the camera is having trouble communicating. It usually means an incompatible 3rd party lens or slightly dirty lens/camera contacts. (Although sometimes it seems to indicate a problem with either the lens aperture or the camera shutter.)

For an incompatible lens you have to have the manufacturer replace the electronic chip in the lens.

You can clean the contacts with a pencil eraser if you are careful (and have the lens and camera openings facing the ground when you do the cleaning so eraser crumbs don't end up in the camera).

The 'busy' error likely means a problem with the memory card. Try downloading using a card reader. If the download is successful be sure you format the card in the camera before you use it again.

It the error keeps occurring you may have to have the camera serviced.