Hi JoeC. Microsoft say that this is caused by one of the following:
The amount of space on the hard disk has been reported incorrectly.
You installed drive overlay software, but you did not follow the correct installation sequence. For example, you may have to press the SHIFT key or use a similar keystroke combination to start your computer when you use a disk.
The computer has a virus.
The computer has failing or faulty hardware.
click here;en-us;289727 or
htt p : //support.microsoft.com/default.aspx?scid=kb;en-us;289727 ( I hope the spaces will prevent the link being corrupted)