When I start Custom Clean I get a message to close Avast Secure browser. When I try to continue CCleaner tries to close the browser and then it asks to try to force close. Forced closure fails. I can only continue when I click cancel.
I also notice that Avast Secure browser cannot be closed in Task Manager. Access is denied.
I will be happy to provide details. I am using Windows 7 Professional 64-bit.
This appears to be due to the Avast Self-Defense module, which is designed to prevent malware and other bad actors from closing the Avast software (more intended for the antivirus software, of course), as described in this discussion: https://forum.avast.com/index.php?topic=220629.msg1469867#msg1469867
The linked message specifically lists a process that may prevent this from occurring. Another process was listed here: https://forum.avast.com/index.php?topic=220629.msg1526209#msg1526209
(In short, CCleaner is not working as intended here because Avast Secure Browser is working as intended; the Self-Defense module is preventing another program from closing it, seemingly the same with Task Manager. As such, a workaround would need to be taken to prevent that intended behavior.)