I experienced a spontaneous Err99, with my 10D, followed by complete non-functioning of the autofocus. No focus points, only manual focus! I only use new Canon USM IS lenses.
This solution came from from Canon eCare USA: Thank you for your inquiry. We are sorry to learn of any difficulties you are experiencing with a error 99 on the EOS 10D. You may want to try resetting the camera. Set all Custom Functions to the default position. Take the battery out of the camera, let the camera sit for 15-20 minutes. This should reset the memory. Replace battery and with a dry cloth clean the lens and camera contacts, to get a full connection and attach a Canon lens. My 10D works perfect again since then! Marius * **** ******* *********************************************************** * For list instructions, including unsubscribe, see: * http://www.a1.nl/phomepag/markerink/eos_list.htm ***********************************************************
