As you should have permission (based on your game registration) something went wrong with the forum permissions of your account.
To fix this, please send a ticket to the Helpdesk (link found at the top of this page). They usually fix this in 48 hours (though weekend probably already started down under).
This seems to have happened a lot, so please-o-please send a ticket to the Helpdesk about this as the more people do, the more likely it is they are going to do a structural fix (instead of moderators keep taking the blame for this silly technical registration problem).