my son has a canon eos d400 and it was showing an error 99 i spent a few hours working it in different modes and found that the lens set at 55 there was no error in auto and went down to 25 26 at 24 it showed error 99 so figured it was the lens took the lens off and placed a piece of very thin paper over the lens contacts and fitted lens ,and in all modes the camera is working perfect ,but you must focus manual i will buy a new lens for him ,but wil test it on the new lens first