Error 99 is not specific. It just means something is wrong and the camera is unable to function, but doesn't give any clues what the fault might be.
I agree with cleaning the lens-to-camera contacts and the idea of trying the camera with another lens and the lens with another camera, to see if you can determine which is at fault.
It also may help to reboot the camera and/or reinstall the firmware. Maybe something has gotten hung up in memory or some instructions have gotten corrupted.
To reboot the camera simply turn the camera off, remove all batteries (including the small time/date battery), turn camera on and press shutter release button once (nothing will happen, this is just to clear any remaining power stored in the circuitry). Then turn the camera back off, reinstall the batteries, turn camera on and check the date/time. If it needs resetting, then you got a proper reboot. You likely will need to reset things in the menu and the custom functions.
While doing the above, it's a good time to replace the time/date battery. If your 30D still has the original, it may be sorely in need of replacement. Those little silver button batteries are widely available and easily found.
To reinstall the firmware, go to the Canon website, search for 30D model and look for the software page. The latest version of firmware should be available there for download, along with instructions how to install it. Follow the instructions very carefully. It's not difficult to do, but must be done right or there's risk of "bricking' the camera.
There's no guarantee that either of these will help... but they might, plus are free and relatively easy to try yourself.
If none of the above helps, you'll likely need to have the camera looked at by a professional repair tech.
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Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7D(x2), 50D(x3), some other cameras, various lenses & accessories
FLICKR & PRINTROOM
