Can’t use admincp after fresh install

[Kyttias]

1) What does the line you changed look like now so we can confirm it's correctness?
2) Using "RewriteBase /" will break everything. Don't do that. The base for rewriting must be routed through the index and no changes should be made to that file unless you know what you're doing. Things are probably not working because the changes from 1 are wrong.
3) That's because because of 2.

So, undo all changes. In 1 I believe the line should be:
$this->root = "/home/yoursitename/public_html/members/mysite/";

I still don't know what your site name is, but you get the idea?

If it's not what you have, what do you have? I'm pretty sure all the rest of the errors revolve around this.