After running v3.17.1689 I cannot log out and log back in, or switch users. Rebooting restores this ability, but running CCleaner again will bring about the issue.
Running MS Windows XP Professional 32-bit SP3, 3.4 GB RAM and 34% Free HDD
There is nothing in the cleaner section that would do that
Did you use the registry section? Are you using Winapp2.ini or CCleanerEnhanced (the latter is not supported here)? Did you add anything to the includes seciton?