Hi Eddie
The message means that there is an error on your computer hard drive and Chkdsk means Check Disc on the F drive of your computer. Try this:
Ensure that no programmes are running on your computer and click on the "Start" button.
Click on "Run."
Type "cmd" into the Run window and press the "OK" button.
Type "chkdsk x: /f" into the command prompt, where x: is the drive letter of the drive that is giving you an error when you try to defragment it.
Press the "Enter" key to run chkdsk on the drive. If you are told that you must restart the computer to run chkdsk, type "yes" and then press the "Enter" key. Restart the computer to run chkdsk, and then you can defragment the drive.
Hope this helps