A new version containing the updated version from ArkServerAPI.
You also have to update the Permissions Plugin to get this working again.
With this new Versions, you need to have the Permission Plugin installed.
Once you have done this, you can also use Permissions to allow joins.
There are 2 possibilities:
1.) Give the group the permissionExclusiveJoin.Allow
to allow exclusive joins
2.) If you want to allow join for everyone, you need to addExclusiveJoin.Allow
to a group namedGuest