Goin' nutz with the ERR99 code with my Rebel XT

Just recently, started getting the ERR99 code on my 2 year old Rebel XT. I've tried removing the battery, cleaning the contacts, etc. But yesterday on a trip to the zoo, it started up again. I was using a Tamron 75-300mm lens (which I have had nothing but good shots with since I bought it over a year ago). After about 5 shots, BAM!! There it goes. I tried turning off the battery, removing the lens and reattatching it, but it kept on acting up. ONLY when I turned my camera to the sports icon, did it seem to help. That only made me more confused. I would try to change the mode, but would get the code again after a few shots.

I am at my wits end. I suppose I could send it off and see if my repair shop can figure it out.

Any help you can offer would be great!!

Thanks

Actually, my photos are now at:

http://www.flickr.com/​people/dougbrownphotog​raphy/

Doug before you have it checked out you might wanna take out the small lithium battery also. Let it sit for several minutes before reinserting.

Does the camera work OK with other lenses? Your 75-300 lens may be the issue - perhaps a sticky aperture diaphragm. I had a similar problem with a Tokina 24-200mm. Try using the lens in Av mode with the aperture wide open and see if the errors stop. If you only get errors when the lens is stopped down, this could be the problem. Another test is to use the DOF Preview button and check whether the aperture closes down completely and smoothly every time. If it works OK wide open then you'll need to have the lens serviced.