When playing co-op mode we cannot seem to play any level except thorns castle, we have completed it several times but the game then ends and there are no other levels in the list. I have read the manual several times and cannot find any special instructionsfor plauing co-op or how to progress levels.

I believe you actually have to finish the other levels in story mode before they become available for coop.

---

Ranked #1 in Kameo overall.

My Website

I have actually completed all levels except the last one in story mode, cant quite beat the final boss.
Do I have to play co-op as the same user or something?
doesn't mention any of this in the manual.

Yes, you have to play coop as the user that finished the corresponding story mode.  Also, if you are having difficulty with the final boss and need some help, you can checkout my boss battle videos here.

---

Ranked #1 in Kameo overall.

My Website