Canon's digital single-lens reflex (SLR) cameras display an "Error 99" code as a generic warning for a variety of camera malfunctions. Improper battery insertion, corrosion on lens-contact points and defective media cards can prompt the camera to report this error message on its LCD screen. By examining and troubleshooting the areas on the camera body that come in contact with accessories, such as batteries, media cards and lenses, you are well on your way to clearing the "Error 99" message.
Set the camera's power switch to "Off."
Slide the battery door open. Press the small tab at the base of the battery down to partially eject the battery.
Remove the camera battery and then reinsert it, making sure it slides smoothly into place with the metal contact points touching the contact points inside the camera's battery slot.
Close the battery door. Turn on the camera to see if the error code has cleared.
Turn off the camera.
Slide the media card door open. Gently push the card into the camera until it clicks and partially ejects.
Take the card out of the camera and then reinsert it, following the diagram on the media card door or in your owner's manual. Close the media card door.
Turn the camera on. Check the LCD screen to see if the error message has cleared.
Turn off the camera.
Hold the camera lens with your dominant hand.
Press the lens release button on the front of the camera body, near the base of the lens, with your other hand. Rotate the lens counterclockwise to release it from the camera. Set the lens aside.
Rub the eraser end of a pencil on the metal contact points on the base of the lens. Use a circular motion to rub away any dirt or corrosion.
Place the lens back on the camera body, aligning the red dot on the lens with the red dot on the camera body. Turn the lens clockwise until it clicks into place. Switch the camera on and check for the error message.
If troubleshooting the camera does not clear the "Error 99" message, the camera's software may have defects. Downloading the Canon Firmware Update 1.0.3 from the manufacturer's website can remedy the error code.
You will not be able to take or review pictures on your Canon camera while an "Error 99" condition persists.