When we went for a non-death quest in "Into the Black Forest", we could not join the game after both of our mates prepared. We could saw everyone was ready on the team screen but it still showed "waiting for mates".
You can usually clear this by disbanding and re-joining the team if it was a glitch in the co-op code. If you can't run the adventure on your own, email your problem to support@cardhunter.com and they can reset the adventure for you. I hope this helped.
