I used my thumb drive with my printer while I was scanning (which i have done many times). This time when I brought it back to my mac, I got an error message that said: "Disk Insertion: The disk you inserted was not readable by this computer. With the options to Initialize, Ignore, Eject" When I go into disk utility, all of the options to repair/verify, etc are all greyed out. I don't want to lose all the files on the drive. Can anyone help?