HM Dungeons - Doors closed....why?

I've played through the hard mode missions and turned in the book and am now working on the dungeons. When I party, all the doors are open as they should be, but when I try to H/H, many doors are closed, not letting me access further into the dungeon.

What gives?

Be sure to have the corresponding quest in your Quest-log. This might do the trick.

Make sure you have the quest which you need for that Dungeon. Also if its Slavers' Exile make sure you completed a time for heroes.