I've just picked up a new 100mm f/2.8 MACRO USM lens and was testing it when my 10D locked up and flashed Err 99. The body was in Av mode and the lens trying to focus on an object about 6 ft away while set at f2.8
Removing the lens and turning the body off and then on again fixed the problem, but left me wondering.... Why did this error occur and is it likely to happen again? I haven't seen this with my other lenses (24-80mm and 70-200mm f/2.8) . Reading a few of the web forums, it seems most occurences happen with third party lenses... Any ideas?
I experienced the exact same problem yesterday with the Sigma 105/2.8 EX macro lens on my 20D. I'm still using the old 1.0.2 firmware as this was the first time I've experienced a problem. I tried a couple more times with the Sigma, but it would always result in an error 99. Apparently this is common and Sigma will upgrade for free, but it sounds like you were using a Canon lens.
-- - Marius
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