I ran into this problem yesterday with version 5. So I uninstalled ver. 5 and installed ver. 4.16. Still had the problem, it would get to 37% and stay at 37% for a long time. So I checked out Task manager, tab processes and noticed that I had several dllhost processes running at the same time. So I searched the internet for some answers. Well it seamed that I might have a virus "poweliks",
Down loaded ESETPoweliksCleaner. Ran the program, and sure enough it found the virus. I also down loaded temp file cleaner, then cleaned out all the temp files. Now CCleaner runs like it should.
I will point out that I was having a few other problems, i.e. I couldn't down load any thing from the internet with out going in to internet options/security and reset to default settings. My OS was Win 7, IE 11.