This happens quite often when a virus/trojan/etc. is on the hard drive when Windows creates a Restore Point.
Just right click on My Computer, Properties, System restore, and check the box to not use System Restore. Click OK, the reboot.
All your Restore Points should be gone. Run your AntiVirus scan, and it should not show any problems in System Volume folder.
If all is OK, then re-enable System Restore.
I have a trojan horse that I can't get rid of, is VB.EN and is it in the systen volume folder. please advise