On my systems, typing in all upper case, or mixed case, makes no difference - nothing happens. Same result when I tried from the CCleaner folder, and from the root of C drive.
I am running XP SP2, with all current patches, TrendMicro OfficeScan and Windows Defender.
Over the last year or so, I have tried on several occasions to get the /AUTO parameter to work, to no avail.
Could it possibly some kind of rights or permissions issue? I use the Security Configuration Analyzer (an MMC plug-in) and a security configuration template published by NSA, to harden my systems (disable anonymous access, null access, user account enumeration by anonymous users, etc.). I don't normally have any problems, and it really cuts down on network-based attacks from infected machines. I did, however, find that PageDefrag requires that administrators have debug rights, a slight variance from the NSA standard template. CCleaner runs fine with the GUI.