As of 9-13-16, the CCleaner setting "Skip user account control warning" is not working with Windows 10. When trying to check the advanced option "Skip user account control warning" I get the message "system cannot find the file specified". This originally happened with CCleaner version 5.22.5724 (64 bit). I uninstalled that version, and I reinstalled version 5.21 to see if that would work with the "Skip" advanced option. Unfortunately, version 5.21 also yielded the "system cannot find the file specified" message.
It appears that perhaps Windows 10 moved or removed the file needed to activate the "Skip user account control warning".
Perhaps you can find another reason that the CCleaner setting "Skip user account control warning" is not working with Windows 10.
Have a look in Task Scheduler (type "Task Scheduler" without quotes in the start menu if you don't know how to find it, or right click the start menu and go into computer management and it should be listed in System Tools) Navigate to the Task Scheduler Library (withing Task Scheduler), and look for the task "CCleanerSkipUAC" task. (FYI, this is the "file" needed to activate the "Skip user account control warning").
If it appears, great try disabling and enabling the task (or just enabling it if already disabled).
If it is NOT in the Task Scheduler list navigate to "C:\Windows\System32\Tasks" in explorer and see if there is a file with that name, and also check "C:\Windows\System32\Tasks_Migrated" for that file (if not in the first location). Try to Copy it somewhere else, you'll likely get permission errors and be unable to copy it if so try moving the file instead. This file is simply an xml file without an extension, the idea here is to move the file out and then import the task into Task Scheduler by selecting import a task in Task Scheduler and selecting this file. (it won't work if the file is in the windows directory though).
One of two things is likely to happen, after doing these steps, upon trying to disable/enable the task or importing/creating the task you will get an error saying something along the lines of it can't do it because it doesn't have permissions to update the task or the task already exists, if you don't get an error it's probably fixed. Should you get the error then, the issue is due to task corruption and the solution is within the registry see this rather old page for details on how to fix it. https://support.microsoft.com/en-us/kb/2305420. And feel free to rant and rave at Microsoft (on their site) if it is this issue.
Yeah it's a Microsoft Issue. I had the same problem after updating to win 10 from 7, and many people seem to also get it if they roll-back to win 7 from win 10. Anyway glad I could help.