It’s quite common for Canon DSLR cameras to get an “Error 99” message. Some say it’s a memory card error, others say it’s related to the camera battery. The truth is that it could be one of two or several other problems that could be related to either the camera body or the lens.
Here are some tips to help you diagnose error 99. These tips assume that you have already tried a different lens (from the camera manufacturer) and a different CF card (freshly formatted).