403 Forbidden nginx? CCleaner Will Not Clean It?

I did some research and I found this error on certain websites was due to a registry error. When I run the registry fix in CCleaner, it is not fixing the problem. The fixes online want you to download another software just like CCleaner to fix it. I would rather not do that, but I would like to know why CCleaner can't fix it. Anybody got a clue? Thanks!

As far as I know that is a server side error and not a user (you) error.

The website admins need to fix that error on their site, not you.