After it failed to open the admin page with the status message that it was denying access did you refresh the entire WP admin (i.e., select a different option from the WP menu at the side? This would reconstruct the entire menus and we could see if the forum menu had expanded. I am guessing they probably did but you didn’t do this. Which would be understandable.
And – what does this message look like? Is it the standard WordPress denied message that displays the cryptic message in a light grey box central and near the top of the screen?