We had a team of 5 lined up to play Midnight from the Iconian arc. As soon as the we pressed the Begin button and accepted the away team we crashed all the way back to the desktop. All of us except the one in a different instance.
We logged back on and it happened again. After that we disbanded the party and each of us ran it solo with no problems.
Second time we were unable to play a mission in the Iconian arc but the first time the problem was so immediate and dramatic. The previous problem was Broken Circle where M'tara would not spawn in the final room after the cutscene. Again, it worked fine solo.