My hero Siouxsie had just finished Buried Dungeons, got all the gems and tried to enter the Treasure Room after the door had opened in the normal manner.  On trying to enter the treasure room to collect my reward I got a critical error.

I logged back into TTJ but could not get into Siouxsie as it would not load properly - fogged out screen and the hour glass showed continually.  Had to get out of the game and close down the window from the game icon pinned to my bottom toolbar using right click.  I tried for a second time 15 minutes later and still got the same failure.

For my third attempt I loaded TTJ and changed heroes entering Dordiana which worked as normal.   From there I was able to log back into Siouxsie and return my hero and army from Buried Dungeon.  Siouxsie is now functioning as normal. 

I have not received my reward for completing Buried Dungeon and will not return there as Siouxsie until told it is safe to do so :)