Mega, the reason your PM inbox became overfull is because you were removed (by request) as a moderator in the Creatures section. It was never promised that the enhanced permissions (i.e. PM storage) that came along with a membership in the moderator usergroup would be permanent.
Nevertheless, I have applied a 3 year Modified membership to your account, which includes storage for 1500 private messages, in recognition for your contributions to the Creatures section.