Could the key have been deleted on purpose to prevent people from accidently compressing the drive and messing things up? I'm no Registry expert either. There's an Undo for the file you ran, here so you might want to run that one. And it's not just removing the minus sign... Caveat emptor! :emotion-5: Ron  
I am using a Dell PC with Windows XP SP3. The "Compress old files" registry key was accidentally deleted. How can I restore it?  Thanks!  
Disk Cleanup