As I understand it, in Windows, System Restore is part of VSS see here
. After XP the way this worked changed and in Vista and Win7 System Restore works differently . For OTL to work SR must be enabled and functioning; if not, the restore point creation will fail. You will see a line in the log stating the success or failure of the attempt.
Because of the differences from XP on Vista and Win7 systems you will not be able to clear previous restore points, this will need to be done manually through System Protection if you want to do that. If you use CLEARALLRESTOREPOINTS on these OSs it will only create a new restore point.
My first thought when you asked the question was that you didn't have SR enabled in your machine. As you state it is and you are running OTL as administrator then we need to look for a possible reason why it isn't working. It may be that you are seeing that OTL is not clearing previous restore points on Vista and Win7 in which case the second paragraph above will have answered your question.
Alternatively, if OTL is not creating a restore point, then your security programs might be interfering in some way, there could be corruption in your system or maybe there is some malware causing the problem. If this is the case then my suggestion is that you open a topic in the Malware forum and see if someone there can help you.