Hi Hazelnut,
I am experiencing the same issue. I ran ccleaner, I have System Files - temp files set to delete. I ran it, and nothing got deleted. I then rebooted, since I read on a different threat that when a file cannot be deleted it is set to delete on next reboot. I rebooted and nothing happened. Unless I'm supposed to check mark that option, but I cannot find anywhere that says, "Delete on reboot". I am checking the following location C:\DOCUME~1\username\LOCALS~1\Temp
several files with the extension .tmp and a messenger cache folder is still sitting there. Not to long ago I installed a new HDD, so I know my Windows is free of issues since I haven't installed anything or unistalled anything of the normal use. I noticed this has been the case in previous versions as well.
OS: Win XP SP3
CCleaner v2.22.968