Though I don't understand fully the original questions,t but my situation is almost similar. Which is, after my son saved all the jpeg files from his Mac into a pen drive, I cannot open all the files using a Windows PC. Whenever the pen drive is inserted into the PC, it will ask whether to proceed to reformat. Other than this message, it does not display other info. So, there is no way to copy back to hard drive - as one has suggested. Thank you.