I posted this solution last month in the BIO forums...I hope it helps since is very easy and it doesn't require any special actions which might mess up your game.
"Hi all,
I know is probably too late for most people who play NWN the solution I provide, but here it comes...
In order to get Lenton's attention and get the reward after bringing the Troll Chieftain head to him (or receive the quest alltogether) all you have to do is:
1. save the game while standing next to him
2. reload the game and press the "pause" button just before the game is completely reloaded (therefore the game will be paused when the in-game screen will appear - it is possible to do it since I did it many times)
3. "talk" to him while the game is still paused !!!!! it should work now fine...
No need to debugging nor charming/dominating him. He will take the head from your inventory unlike in the case of a charming/dominating solution...
Cheesy? Maybe...but it does the trick...
The game will continue without any problem and if other NPC's in the game will have the same problem...you know now how to solve it.."
good luck!