Users can't log in or post even though usergroup permissions are set..

[Lena Starling]

-EDIT- They're able to log in through the forum home now. It was just VBadvanced they couldn't get through..

But the posting problem persists. I've been getting a lot of complaints from my members lately about using the Quick Reply and Reply buttons. None of their posts will show up.. They may every once in a while, but most of the time none of them can get their posts through. I'm seeking help with this problem because I'm clueless right now. I've checked all forum permissions and usergroup permissions and everything is set the way it used to be. What could be going wrong?

Well a user just explained the problem to me in more detail:

- She was viewing a thread that I'd posted and everything was going fine. She posted in the thread and it showed what she posted.

- But when she checked the new posts it showed that she didn't post.

- And when she went back to the thread the post wasn't there anymore.

So basically the posts are.. vanishing, and no admin has touched them. Help? I'm hoping this is something that can easily be fixed