I am playing as vikings on hard and the campaign is good fun; raiding rakes in cash

The problem is I can't build the titles line of buildings in Norway. I have built Royal Court to get Jomsvikings, but I still can't build Royal Hall. According to the tech-tree the only prerequisite to Royal Hall is Drinking Hall (and the Royal Court is like lvl 4 Drinking Hall). Anyone who can explain this for me?