From the Garmin Website:

Check a Garmin Mass Storage Device for Errors

A check disk is run to ensure the integrity of the files on a device. To run a check disk:

PC:

Connect the device to the computer
Press the Windows key + E
Locate the Garmin device and see what drive letter Windows assigned to the device
Press the Windows key + R
Type cmd
Click OK
Type chkdsk x: /f (Where 'x' is the drive letter assigned by Windows)

The check disk will now run on the Garmin device

Answer Y for Yes if you are prompted to convert orphaned fragments into files


Contact Product Support if you receive the message "The type of filesystem is Raw. CHKDSK is not available for RAW drives."