Unable to remove infections, can only work if restarting the computer?

I have Ad-Aware 2007 (free) and I just full/smart scanned my computer and tried to get rid of the infections by clicking the remove on and then a pop up comes on that it can't remove if infections unless I restart the computer. Subsequently, I restarted and have to scan all over again. Yet, it still doesn't work. My computer is Windows XP 2005 edition.