memory cards says needs to be formatted, but took pictures yesterday with it

[huntorama]

Took pictures with Cannon Rebel T3i on Saturday, on Sunday went to upload them and memory card states it needs to be formatted?  Only thing that happened with camera was took pictures, came home and put camera on table and tried to upload the next day.  What happend to the pictures I took?

[cicopo]

The most likely explination is that something interrupted the write session so a file hadn't finished writing. This causes card errors but you may be able to recover the files (other than the bad one) using a recovery program. Things that might have been the cause are opening the card door, weak battery, turning off during a write session (saving photo files from the buffer to the card) or maybe a bad card

[huntorama]

Thank you for responding, I wonder if I can get the pictures back and the battery was running low so maybe that is why?  Can you recommend a free recovery program?

[cicopo]

Take a look here

http://photography-on-the.net/forum/showthread.php?t=670801