Commander Ralph should have given you an invitation to the castle when you spoke to him again after killing Cybu. If you've got a lot of stuff in your inventory, it may be hidden under something.
You'll also get two more invites to the castle, one when you complete Captain Mitox's two quests against the orcs, and another one when you solve the mystery behind the plague. So don't worry, sooner or later you'll get your invite.
Cheers <img src="/ubbthreads/images/graemlins/biggrin.gif" alt="" />
