The problem arises when a new member has fewer than 5 posts. The Guild has has some problems in the past with spammers joining up and plastering the forums with junk. In order to put a stop to this, we have instituted a requirement of having 5 posts before the forum will let just any post through. MOST new posts do make it through anyway, but sometimes the filter spots something and drops that post into the moderation queue. Outside links or long posts have a tendency to trigger the filter. The 5 post requirement is also in place for sending/receiving PMs as well as having viewable albums, and for mush the same reasons.
I hope that clarifies things.