You can only carry one trophy head at a time, if you still have Nadir's head, turn that into the Royal Huntsman first.

I think the trophies don't disappear or decay (unless other items), so it will be there when you come back from your visit to the Royal Huntsman. I had a similar issue later in the game. It's a bit annoying when you can only one at a time but the super-monsters appear in very close locations.

I don't believe I *do* have anyone else's head in my inventory... at least, not visible.
What I *do* have, is *four* of those dice boxes, none of which can be dropped!! I wonder if that's the issue??

I'll go and talk to RH, to see if he'll take anything off my hands.

Later note:
Nope, I don't have anything that he'll accept. I wonder if I'm simply supposed to do the "Monster by the Lake" quest first??

Well, it ended up being irrelevant, I pursued the main quest and am in Vizima now.
I *think* I did the Royal Huntsman tasks out of order, probably had to do the Nidal one first, before I talked to him.

1: In your inventory, it goes directly onto the hook on the bottom right. (see pic)
2: The dice are not an issue, you can't drop them because they are quest items.
3: It makes no difference which quest you do first, the attached pic was doing Ozzrel first. It's not really irrelevant, if you complete all the Royal Huntsman quests in each chapter, he will reward you with your choice of one of the two best swords in the game.

hmmm... well then, I'm still confused. I did *not* have any other head on that hook, yet I could not pick up Ozzrel's head... it just said 'inventory full'. I could not get the quest to proceed any further, by talking to him. He was telling me to do the first quest, but when I went to the appropriate area by Miller's Building (don't recall the name), at night, no named creature appeared. It appears to me that I had simply stumbled into a bug in the quests??

That's sad, because it means I won't be able to get that sword at end of game... sigh.