It seems someone else found a solution and it was to do with the Sylannas Loyalist questline.
I found the solution for this with a friend, it appears that if you did Sylvannas loyalist quest and then faction change to alliance you complete the scenario there again, when you transfer back to horde it does not see you did loyalist quest.Solution is eitrig quest where you help him out of ogrimmar, is available and you can then do the scenario a third time! i found eitrig in ogrimmar and did the quest with him then went through saurfang side chain quest.