I bought a SIGMA 70-300 F4-5.6 APO MACRO for my duaghter for her to use on her Canon EOS 350D.
When the lens was put on the camera it came up with ERROR 99.
So, I tried the lens on my Canon EOS1D MKII and it works fine.
Then I put the lens onto the 350 again but not all the way. Switched on the camera and fully locked the lens in. This time it worked, auto focus, no problem. But, when I tried to take a photo the shutter operated and then ERROR 99 appeared. Switching the camera on and off has no effect, niether does removing the battery, memory card etc and re-inserting them.
If I do the above so that the lens operates on the camera, but do not press the shutter, and then switch the camera off and on, ERROR 99 appears.
I have cleaned all contacts, and all other lenses I have work on the 350D.
Thought it might be a firmware problem, checked that and it has 1.0.3, which after searching the internet seems to be the latest version.
Any ideas on this problem would be very much appreciated.