Hello,
Thank you for your reply, Andavari.
No luck with the task manager.
I was familiar with Revo. Unfortunately, neither Geek nor Revo uninstallers managed to fix the error. They do find some remaining files (I doubt they find all of them, though) and they do appear to remove them, but once I download CCleaner from its site again, install it and try to run the uninstaller, I'm getting the same NSIS error.
Should I go back to some older versions of CCleaner? Or that won't solve anything?
I'm lost here. Don't recall having such trouble with uninstalling CCleaner ever before.