Doing the opening Dark Brotherhood quest (assassinating three different targets) and the quest to kill Ennodius Papius will not register as complete when I kill him......I tried reloading earlier saves even saves before accepting the contracts and it still wont update. I will be very angry if I cannot complete the dark brotherhood quest line because of this. It seems not even keeping multiple saves can save you from this buggy mess.

Have you tried all the dialogue options with him?

No, first time I killed him I remained silent. Second time I killed him without him even noticing me. Third time I killed him well he noticed me but I did not talk to him. Fourth time I tried soul trapping him as I heard that works but it didn't. I guess I will try other dialog options and see if that has anything to do with it. Thanks for the tip.

Np. For the record I used 'You should be paranoid...' as my dialogue choice and I had no problems.

I tried all three dialog options and he is still bugged. I also tried killing him in more various ways, I killed him with a shout and it didn't work. I killed him with magic and it didn't work. I killed him with an unenchanted weapon and it didn't work. Luckily I looked on the wiki and it seems I only need to turn in one of the contracts to advance the story, not being able to kill him just locks me out from doing that contract and the mourning never comes quest. While this still very annoying I can only hope that I still have a chance at completing the main quests.

That svcks. Good you can still progress

It only let me do the next step in the quest line and then Astrid tells me to give her time to think and to go get more contracts from Nazir who tells me to finish the ones he already gave me. I then proceeded to try and kill in a series of different ways and the quest is still broken. Did everything I can think of and then some and quest is still bugged. The dark brotherhood and military quest line trophies are the only ones I need to platinum and I am having problems with both. I have to admit the only reason I am still playing Skyrim is I wanted the platinum but oh well. This game has been more frustration than fun and I will never buy another Bethesda game again within a year of the games launch and researching first to see if they finally decided to respect their customers and actually fix their buggy excuse for games after taking our money.

I have the same problem and I can not progress in the dark brotherhood quest.

It is really frustrating because I have about 9 quests locked and unfinishable, not counting problems with houses and other stuff...

I really wish this game had not been awarded Game of the Year. It's so undeserved, it makes me sick.

I had a similar problem with the Companions questline . Unfortunately the only way I was able to fix this was to start a new character .
If it's just the trophy you want , do what I did . Start fresh , do the bare minimum to get out of Helgen . Do not accept any side quests , hell , don't even talk to people if you can help it . That should allow you to finish the questlines , it worked for mine .
Above all , DO NOT complete Dragon Rising , then you won't have those (self censored) creatures bugging up your game .

hopefully it will be patched in the next patch..im stuck with my main char aswell cause of this