How do you unlock these? I'm at the main quest line where I need to do the one for level 50. I did the first guildhest (the enemy party) when it came up during the main quest line (level 10 or so) and figured I had to unlock them in order when this one popped up. So I found the list of them and went to the second guy on the list but he doesn't give me the second one to queue up for and I can't seem to queue up for the first one anymore.

Any help? =/