It's not reliable. Sometimes it works, sometimes not.
Another suggestion for you, Tech:
May be the diskspace for restore points on your system is too small (I had that problem also some time ago). Just go to "System Properties" and hit the tab "Computer Protection". There you can adjust the space reserved for restore points and give it at least 10% of your disk space for every partition.
A common thing with windows is also:
If you try to restore a point which is let's say the 10th oldest in the list, sometimes it's not even available anymore although it is listed!
If that does not help I've got no further idea about your problem.