If you load an old save does the neck slot function properly?
Alternately, if you start a new game can you check the merchant in Farglow and see if he has an amulet you can try? You can switch initial classes and sell the starting weapons (once each).
Can you click and drag anything out of the slot, even if it is shown as empty?
Does a necklace you right click equip, or drag to the slot, just disappear?
Can you left click on the slot to get a list of necklaces?
For the PC version, if you have the Developer's Cut version of the game, you can open the save in the Developer Mode, open the cheat window (F11) and give yourself replacement amulets to test with. Use the give_set function, or there is a unique necklace near the bottom of the 'give' list (scroll all the way to the bottom -> Mister Necktie, req level 16).
