The Shard's Landing group mission Calling Phantasm currently is bugged. The last step where you open the chest sometimes has the chest unable to be opened.
The mission is able to be completed but the loot items inside the chest can not be accessed or looted.
SOE is aware of the issue and has developed a fix. It is not known if the fix will be ready in time for the expected December 12, 2012 patch or will have to wait beyond that date.
Should you do the mission and encounter this problem, it is suggested you /petition for redress.