Though certainly an improvement over the fickleness of film, the memory cards in digital cameras still aren't perfect. Canon memory cards can malfunction or become corrupted, preventing you from taking more photos. Fortunately, many common memory card errors are easily fixable. Most errors should not affect the long-term performance of your camera or necessitate costly repair.
Note any error messages your camera displays. Canon error codes are usually two digits and can be used to quickly narrow down the scope of the problem. Many sites online list the cause of Canon error codes (see "Resources").
Take the memory card out of the camera and check for any connection issues. On a CompactFlash card, make sure the pin connectors are clear of dust and debris. On a SD or MiniSD card, make sure the electrical contacts are clean.
Check the memory slot on your Canon digital camera to make sure there are no issues. On cameras that take CompactFlash cards, make sure none of the connection pins are broken or bent. Contact cleaner spray may also improve the camera's connection with the card.
Connect your memory card to your computer and see if it is readable. If it is, check if the memory card is full. Full memory cards are a cause of some common Canon errors.
Insert the card into your camera and delete all files (if the error persists). Corrupted files or file structures can result in errors.
Use the reformat function on your Canon digital camera to reset the card's settings.
If reformatting does not fix your camera card, it's likely the card is broken or damaged. If you have files on your camera that you cannot read but do not want to lose, consider using a restore utility to recover your files before reformatting your card.
Reformatting a digital memory card removes all data.