יש לך WINDOWS VISTA?
ראיתי את זה באיזה פורום:
Boot from the Vista DVD.
Click 'Repair my Computer'
At the prompt to select your OS installation, click the button that says 'Load Drivers'. This should bring up a explorer-style drive browser.
Then just right-click on the drive you tried to compress, and deselect 'Compress this Drive', which should still be ticked on. Hit apply, and apply to subfolders/files.
Reboot.