Not sure if it will help you like it did me but I used Oynx to clean up my caches and log files as well as some routine maintenance stuff. Now the lock works on the screensaver. If I had known it would have solved my problem, I would of wrote down what I did with it. Very powerful tool so if you use it, read the instructions and warnings carefully and if you have any fear, back up your data before running it. I've never had a problem with it but I make no guarantees either.

Hope it works for you.........