I am sorry that you are having a problem and the solution provided by Brink has not worked.
I have seen this problem, before, from other members of this forum. One possible cause is that you are are scheduling a automatic defrag, which includes the partition where the restore points are activated. If this is the case, you will have to save your restore points to another partition. You can check on the task scheduler to verify the schedule of defrag. Sometimes 3rd party software, also schedules a defrag, such as and A/V.
I have included information on this problem as provided by MS
Shadow copies may be lost when you defragment a volume
Here is another information bulletin from MS, that may provide you with other information that may help you to solve your problem
http://support.microsoft.com/kb/301224