So i was having trouble with Ennodius Papius, the quest wouldn't update and as a result i couldn't continue the dark brotherhood questline

I carried on playing regardless as i wasn't very far in the main quest, so i went and played a few main quest missions. After completing 'The Horn of Jurgen Windcaller' and starting 'Act II' of the main quest, i tried again with Ennodius Papius. Hit him with a Fus Ro Dah and attacked him, and the quest updated

I know there are a few others who were having trouble with this issue, so i just hope this works for you like it did me. If you've advanced the main quest past that point though i don't know what to suggest