I see that no one here has mentioned proxyban (evil fees) yet. Could it be that the user registered an account from an abused IP range and is required to pay an evil fee in order to post?
No:
It's not blocked or banned or anything.
I can’t think of any reason why someone should have to wait 6 minutes to post after logging in. I don’t think it is unreasonable to believe that someone may read many posts while not logged in, find something interesting, log in, and try to post.
It's probably just a bug that's not really worth fixing, just like logging in for the first time tells you something failed, but if you just registered you can ignore the message (I don't remember the exact wording).