Bravo! and thanks a lot. I was denied access to ACP after assigning forum permissions to a new forum. The above post worked perfectly. I am using Olympus 3.0.9 ProSilver.I had the same problem. I played with it a while and have something of a solution. It involves establishing yourself as a member, then as a moderator, and THEN as the Administrator.
1) Log in.
2) See the screen that says you are now logged in. Wait a moment.
3) It should redirect to a screen that gives you access to the Moderator Control Panel.
4) Click that.
5) Click on Members (top right)
6) Click on your own name.
7) Top middle, click where it says "Administrate User" next to your own name.
8) Sign in again (re-authenticate yourself)
9) You should now be looking at the admin control panel.