Some USB Flash drives have a lock switch on the outside of them (a slider switch) which when switched makes the drive Read Only. If you don't see a switch then try check disk on the drive. Go to Start/Run and type CMD and press enter. In the Command Prompt type the drive letter of the USB drive (ex) F: now the prompt turns to the drive letter (ex) F:\> now type chkdsk /F and press enter. Now type a Y to Unmount the drive. Check Disk will try and fix any file errors.