No Permission to view forums?

[DragonBlade]

Not sure quite which section I should post this in, but here seemed most fitting.

We have a member who is a Moderator of our forum, and recently he has been unable to access anything. As I recently made a boo-boo involving the usergroups of about 150 members, I thought it'd be as simple as resetting his usergroups.

The problem persisted, though--anytime he was trying to view a forum (even one normally accessible to guests), he kept getting a "no permission" error.

We admins logged in as his account and had no such errors, no problems whatsoever.

Another peculiar thing I noticed was that the "Who's Online" was only recording the action of him logging in and being redirected to the index--NOTHING after that (except when we admins were on his account).

The situation changed when we added him to the Super Moderator and Administrator usergroups. He was able to use the forums as normal, then, weirdly.

We of course tried disabling plugins to see if that was affecting anything.

Is it possible that his ISP is caching our forums, maybe, and that him logging in as S-Mod or Admin somehow bypasses that? Or is it more likely a problem with our own forums? I honestly can't see how it could be the latter, but I'm stumped.

-Sarteck