It is important to understand what type and quality of card that was purchased. For example, some customers will find great deals on "large" CF cards that are multilayered. A multilayered card is a card that consists of 2 or more smaller cards sandwiched to make a larger megabyte card (4x256MB = 1024MB or 1GB card). While these multilayered cards work great when purchased, they seem to become unstable after repeated usage. If possible purchase single layered cell cards. They were intended from the beginning of manufacture to be a certain size and lack the "bridges" found in multilayered cells that can cause corruption on a card.
Four main reasons why memory cards become corrupted:
1. As mentioned above, a multilayered cell card that has images added and deleted will eventually try to save a partial image on one cell and the rest on another, causing corruption of the image or images.
2. Some cards will allow you to keep shooting images even after the counter is at zero. Once the card is full, it might have a small space in which it tries to add an image that is too large, hence corrupting one or several images/files.
3. If the card is ejected prior to having finished writing the information to the card. The card may become unreadable and lose or corrupt images.
4. Like in reason three, the same will happen if the camera loses power from the battery while writing.
How to prevent corruption of your images
In order to keep good "hygiene" on your cards, you should avoid the four points above and do the following: After your images are downloaded to your computer and possibly backed up on some other sort of device (RAID, memory vault, DVD, CD or other harddrive), you should format your card in your camera. This should be done not only once, but three times. This will insure that your card is free from any images, markers, folders, partitions etc. (when we recover cards for our customers, we can read 80% of the information after 1 format, 40% after 2 formats and 0% after 3 formats).