I have the same issue where I can't resize the window. I tried deleting the reg keys like you suggested, but that didn't do anything. My resolution is 1600 X 900. Guess I'll go back to earlier version too. I think there are more users affected than you may realize.
Sometimes I click on the shortcut and nothing seems to happen so I click it again then I realize that I have two instances of Ccleaner running. Could you put in some code for Ccleaner to look for other instances of itself that are running and prevent multiple instances running at the same time? Thank you in advance for your reply.