If you are speaking about the Area quest at the far left corner of Section X, then I would see if the feller up there, bottom left edge of that map, will let you re Accept it, otherwise that place is a daily so you can try your luck the next day.
Sorry, I know this may not be the most helpful reply, But I do know some of the quests in those lvl 50 areas can be some what buggy at times... so you may be dealing with that problem .
Other solution may be to restart you game I know that helps me with some of my problems.
If non of the above help, then visit this link : Section X Dailies Guide
and see if that helps you gain more information on how to regain the quest.