CCleaner and slow registry clean

Hi,

i have installed CCleaner on all the PC into an italian public Library.

The o.s. is windows xp professional sp2 + OpenOffice 2.4 + Mozilla firefox + Java 6 up.5.

When i scan the registry to find problems, CCleaner stops at 18% for 1-2 minutes, then restart and complete the 100% scan.

To avoid this problem, i have to switch-off the "ActiveX and class issues" box.

Why??

Thanks.

retegraf