Problem solved: answer was online already for vista.
Windows Vista and volume shadow copies
The System Restore process in Windows Vista regularly creates volume shadow copies, which are essentially snapshots of system activity stored on the hard drive.
Volume shadow copies are automatically deleted when:
The number of shadow copies for a volume exceeds 64.
The amount of disk space allocated to shadow copies is used up.
When either of these conditions happen, the oldest shadow volume copy is deleted.
There is a known issue with volume shadow copies and third-party defragmentation tools such as Defraggler. If there isn't enough room set aside on the hard drive for the volume shadow copies, the defrag process can cause one or more of them to be deleted.
You can delete volume shadow copies manually to free up space and prevent this problem from occurring.
To delete volume shadow copies manually:
Start the Disk Cleanup program (typically located in the Accessories folder).
Select the drive where the shadow volume copies are located (typically, the drive where Windows Vista is installed), and click OK.
On the More options tab, in the System Restore and Shadow Copies section, click Clean Up.
Disk Cleanup prompts you to confirm the action. Click Delete.
