Really Bad Bug. Tested it twice (fresh reinstall of the entire system). This is what happened ...
Notebook (ACER Aspire 7520G) with Vista x64 Ultimate gets upgraded to Windows 7 x64 Ultimate. As the system needed cleaning up, I decided to install CCleaner V2.30.1130 as I had really good experiences with this software under Windows XP Professional (both x86 and x64) as well as Vista Ultimate (again both versions).
Now, once I installed CCleaner (making sure it was in the right directory of course), the trouble began. While opening folders on HDs on the Network, I got the error "Windows Exploerer has stopped Working". Then Windows Explorer closes and restarts. This problem is persistant. I identified CCleaner as the culprit by eventually doing a clean install of Vista x64 Ultimate, upgrading that again to Windows 7 x64 Ultimate and again installing CCleaner, this time the latest version (V2.32.1165). Again the some problem.
I don't think there is much to do about it but reinstall Windows 7, clean this time, and stop using CCleaner. A simple removal of Ccleaner, either through the Control Panel or manually doesn't solve the problem.
Hoping to have been of service.