It's possible that you're using a later version that PartyZone doesn't support yet. If you're using 1.11.1 then please downgrade to 1.8, 1.9, 1.10, or 1.11. The development team are more than likely already working to implement 1.11.1 support, and if not, will be soon. Please be patient as it just came out. I can't guarantee that it will be right away, but 1.11.1 support should come eventually. However, if downgrading your version does not work, contact one of our Admins through the website for further support.