Err 99 on Canon cameras is a non-specific error so it's hard to say what could be wrong with the camera, if anything at all it could be the lens.
I had Err 99 with my 30D which was actually a sticking aperture on my lens. I had the lens repaired by Lehmann and it cost about £120 IIRC that was 5 years ago.
The error can also point to a communication problem between lens and body, sometimes just cleaning the contacts on lens and body can resolve the issue.
Only you can decide whetehr the price of the 20D is worth the gamble. The 20D was a good camera in it's time and well built, but you won;t know how much the camera has been used or how much life is left in the shutter. I'd expect the sensor to need cleaning too as it's a non self cleaning type, though this can be done yourself there are many tutorials on the net.
TBH I'd probably not bother buying unless it was dirt cheap and wanted to gamble it just being dodgy contacts or faulty lens.
Hi all - I am very new to all this so please bear with me.
I have the chance of buying a faulty EOS 20D off Ebay. v cheap.
IT has err 99 when the shutter is pressed - shall I buy it ?
I googled err99 and 20D out of curiosity to see what other things might cause the error.
There is a You Tube video showing a 20D that keeps flipping the mirror up but the shutter doesn't open, only removing the battery stops it. Looks like that camera needs a new shutter, from replies that seems not to be an isolated case,
As Wave said the 20D is an old camera now and the 1000D re-furbished camera on that Canon site looks a good deal thogh not having the build quality the 20D had it should prove just as satisfying to use.