Not a problem. Click "Select All Problems", then click "Fix Selected Problems". If XP says it's invalid, it is. They do have the option, Restore, top middle of the bar, so if you have problems it can put all the deleted bits back in the Registry. I have never had to do this in all the time I have used it. The first run is a bit of a shock, but your PC should run faster. I generally run it once a month, and the usual list is about 18 items. My first run with A Squared turned up 400 + items, and that was a pretty big shock too. Now I get about 10.