Right click on the drive (DO NOT SELECT THE DRIVE) and select properties, then select the tools tab and run error-checking.
Select automatically fix file system errors and press start, this should sort the problem out for you.
If after pressing start you get a pop-up 'schedule disk check' this can be because you have selected the drive, select another drive then right click the USB drive.
USB and Readyboost
Right click on the drive (DO NOT SELECT THE DRIVE) and select properties, then select the tools tab and run error-checking.
Select automatically fix file system errors and press start, this should sort the problem out for you.
If after pressing start you get a pop-up 'schedule disk check' this can be because you have selected the drive, select another drive then right click the USB drive.