Before you send it in, you can try several things.
First, since you say that this is happeing with multiple cards, it's probably not the memory cards at fault. Most likely it's a problem with the camera and the most likely thing with those is a bent or broken pin in the card socket. It can be hard to see a bent pin. Look again, very closely, with a flashlight and magnifier if possible. Also sometimes a pin breaks off inside the memory card, so look very carefully at the business end of all your memory cards, too.
If you are certain the socket and cards are fine, next you could try "rebooting" the camera, which is much like rebooting a computer. This can clear bad instructions that are "stuck" in memory. To do a reboot, turn the camera off, remove all the batteries including the silver memory battery, turn the camera on and press the shutter release button once. The shutter won't fire, but this should deplete any and all electrical charge remaining in the circuitry, resetting the camera to factory defaults and clearing everything from memory. Turn the camera off, reinstall the batteries, turn the camera back on and check the date/time. If it needs resetting, you got a proper reboot. If not, you might have to try the slower method, same as above but just turn the camera on and leave the batteries out for an hour or so while the remaining charge in the circuitry slowly drains. Once again, turn the camera off, reinstall the batteries, turn the camera on and check the date/time. There are no guarantees this will solve the problem, but sometimes it does and it's free and pretty easy to try.
If the reboot doesn't solve the problem, one more thing you might try is reinstalling (or updating) the firmware. Go to the Canon website, download the latest firmware and follow the instructions carefully. However in this case something I am concerned about is that a freshly formatted memory card has to be in the camera while doing the install. I haven't tried it myself, so am not sure if you can use the camera's second memory slot for this purpose. But, if you can, a firmware update/reinstall might solve the problem. It's possible that something got corrupted in the firmware. Again, no guarantees this will help, but it's free and fairly easy to try.
If neither of those help, then I'm afraid the camera needs to be looked at. If you've have it only a short time, the retailer might help you. Otherwise, contact Canon about warranty repair or replacement under warranty.
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Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7D(x2), 50D(x3), some other cameras, various lenses & accessories
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