How do I fix an error 99?

This typically means the camera software does not recognize the lens.

To fix this: 1. Make sure the lens is compatible with the camera. 2. Using the eraser of a pencil, gently rub the contact surfaces clean on both the camera and lens. 3. Remove and reinsert the battery, attach the lens and turn the camera on. This should fix the problem.

Also, Canon has a troubleshooting section for all of their product on the web site.