So you're saying that the error log snippet you posted previously on this thread is outdated ? Then please post another one, when trying the functions with the problems.
As for the rest: please provide the information asked for, concerning the page you get, its full error message and the URL it complains about. A screenshot could be useful, a full copy paste, something. Please also provide information about what redirections you have defined on your forum directory, if any, and eventually unset them, to see if the problem still persist.
It's practically not possible for a standard SMF that the admin pages, if they have the expected URL, that is, forum URL with some action, to give a 404 by itself. I suspect it's trying to get something else, some other page before answering to your browser. And that doesn't happen without leaving a trace. It has to be in the log, as an error, or in the access log, as a request for another page, or on the error page with the address it's complaining about, or all of them.
So: please access the URLs that error out and then post here the error log entries (or attach the error log for that day).
Post here the full content of the page with the 404 error, including the visible URL in the address bar and the URL it complains about.
Tell us what redirections are defined for your forum, be it in your host cpanel or with .htaccess files or any other means (PHP functions for redirecting?) you may have used.