Canon 30D

Bought a 30D, it works fine with the lens, Tamron 75-300 macro zoom, and 18-55 "kit" lens. The problem is the 75-300 will not work in manual, get an "error 99" only when I go to full auto or P will it work. Can this be corrected?

Hard to say... Check the Tamron website or Google for info on possible compatibility issues.

Some older third party lenses do not play well with more recent Canon cameras. There's just no guarantee of full compatibility with third party lenses (there largely is with Canon lenses).

I have a Sigma 28-75 that causes errors and shuts down more recent EOS models, althoug it works fine on 10D, EOS-3 and some other older models. It's not worth fixing. There was a rash of compatibility issues with Sigma lenses and Canon cameras a few years ago... To their credit, Sigma would upgrade many of the more valuable lenses to resolve the problem... I have heard of a few problems with Tamron, but don't know any specifics.

I suspect your 75-300 has an problem controlling the aperture. This is a common incompatibility issue with dSLRs with many older film era lenses (particularly Sigma). I've also had a (compatible) lens with a sticky aperture which acted similar to this. Anytime you or the camera try to close down the aperture, you'll get an ERR99. Try AV mode and snap a shot with the lens wide open then one with the lens closed down to f16 and see if you get the error. You can also look into the lens while pressing the DOF Preview button and see if the aperture is moving at all or whether it seems to be opening and closing inconsistantly.

The only solution, other than only shooting with the lens wide open, is to have the lens updated or repaired. As this is an older lens, spare parts may be a problem.