You haven't by chance gotten a little delete-happy in Windows Explorer lately, have you?<g>

Does it restore to any other restore points? If it does, then that particular RP is corrupt/missing/possessed by Impus Gates-eous (that Little Devil, Bill). Also, if you've run Disk Cleanup you might've inadvertently told it to snag some extra HD space by dumping System Restore Points. In which case, I believe, it dumps all of the Restore points (manually and automatically-created) except for the last automatic RP.

If it won't restore to ANY point, search msdn.microsoft.com for System Restore kb references. You might need (who'm I kiddin'?) PROBABLY need a patch.