Camera Displaying Incompatible JPEG File

Sounds like the card has become corrupted. Did you format it in your camera when you first got it? If not, what you're experiencing eventually happens. Take no more pics until you've recovered any photos that you may be missing, take the card out of the camera. Here's some freeware photo recovery software that should be what you're looking for:

http://camerarepair.blogspot.com/2007/12/recovering-those-accidentally-lost.html

You will need to use a flash card reader with this software. If you don't have one, get one, they're cheap:

http://www.amazon.com/s/ref=sr_st?keywords=card+reader&rs=172282&page=1&rh=n%3A172282%2Ck%3Acard+reader&sort=price

Finally AFTER you've recovered your photos, recommend formatting your card in your camera. Look in the "tools" menu for the selection that shows your card's memory capacity, and select it. Then follow the prompts to format the card. Select "Low Level" format if asked. Note that THIS WILL ERASE YOUR CARD, so again make sure that you have first backed up your photos on your computer.