FWIW:
A DLL (PPCRLUI) can be the problem (http://www.vistax64.com/vista-general/16632-folder-shared-other-people.html)
I have had this problem... CCleaner starts looping at 30% - and never end.
PPCRLUI is a Windows Mail DLL.
I deleted all these TEMP files (after closing Windows Mail) - and CCleaner start working again.