I can't complete this quest unless I choose to lead the two men to the ghost. If I try to deceive the ghost with nekker parts it isn't interactable; there is no option to talk to it. Yes, I have tried different camera angles.

http://www.youtube.com/watch?v=nZzhwiLDvEc at 18:19 displays an interactable ghost. My ghost is not interactable. I have retraced my steps to be that shown in the video, still not interactable. Game is patched to 1.2. Leading the two men automatically leads to a scene with the ghost, thereby bypassing this bug.

I used the nekker parts the first time i played through. The second time i went through i went to the butcher in town for animal parts.

SPOILER

Both times the outcome is the same meaning you have to fight the ghost anyway. Which is rather annoying that in order to even fight the ghost i must talk to the doosh bags again before i try to fool the ghost when i should just be able to say piss off and attack the ghost which is where in the last two tries (nekker parts and oxen parts stiil means fighting the ghost) i have ended up anway.

Try the animal parts from the butcher in Flotsam if that does not work well then i think you might have to reload to a previous save. Not to worry there should be a shit load to choose from, but since the save mechanic is borked finding that right save might be difficult.

hope this helps
Asai

If you have watched the Mythbusters you would know that they use pig parts as a substitute for human skin and organs in testing myths. Maybe you should follow their lead. You might just fool the ghost..

Ghost says you cannot deceive a wraith (he does a DNA analysis maybe? :P) But on the other hand, you can fool the ghost from the banner so it makes me wonder, is it a plothole or is it something else like when a people tries to fool you but you aren't fooled, you say "you can't fool me" but in fact you can be fooled, just not fooled this time.

Turn on ubersampling for just this quest turn in

I had the same problem and this actually worked. I don't have a clue how ubersampling changes things, but it apparently does.