Hi
One or more of the System Restore files could have been corrupted - try
turning SR off/on - but I'm afraid that you will lose any existing
checkpoints:
Right click My Computer, select Properties and then the System Restore tab.
Enable 'Turn off System Restore on all drives' and reboot your PC. After
that 1st reboot go back into SR and disable 'Turn off System Restore on all
drives' and reboot your PC again. After that 2nd reboot you should have one
new SR checkpoint.
Have you got at least 15% free disk space available for Defrag to work?