If you cant accsess the data on that drive and continues to ask to format....
Corrupted Flash drive Data Recovery
What's the best way to get my data off of a corrupted flash drive?
If you are using a flash drive, try and connect it to another computer just to be sure that the USB ports on your computer are not faulty. If you are using removable flash media, try connecting it to your computer with a card reader just to be sure that the cord or device you are using is also not faulty.
Undelete is good for basic recovery on many kinds of drives, internal or external and can handle recovery through corrupted or damaged media. Undelete can recover from any kind of external drive.
If this dont work your flash drive is corrupted and need to get a new one