So I had all the necessary words, but hadn't unlocked any of them. I realized that I had plenty of dragon souls, so I spent a bunch to unlock all the words. I select the mission "summon durnehviir in Tamriel", select the shout, the character starts to say it and...

It cuts off right after the first word.

Apparently I can't complete the missions "learn the first word of durnehviir's shout" and "summon Durnehviir in Tamriel."

Anyone have any idea what's going on?

Do you have any mod's ???

1. There must be sufficient flat space on the ground to summon Durnehviir...and I mean a LOT of space (you also must be pointing towards the ground).

2. Make sure you're attempting to summon him during combat if step #1 doesn't work by itself.

P.S. - You'll soon discover a bug when he is summoned but is banished seconds after...to overcome this you need to summon him and immediately put your crosshair over him (very closely to him) and repeatedly press E to speak to him essentially. This will keep him in Tamriel and he'll assist you in battle.

Unfortunately with all of these inconvenient bugs summoning Durnehviir became a once or twice kind of thing in my last playthrough.