Lua Can't sell/buy necklaces

[Suxex]

Hey, I have a problem with a NPC.. I can't either buy or sell necklaces from him.
When I try to buy it says:

npc.lua:14: in function 'customCallbackOnBuy' 
npc.lua:14: bad argument #2 to 'error' (number expected, got string)

and when I try to sell it appears a "Cancel message" which says that I don't have the item...

The NPC sells and buys rings aswell and it works perfectly.

Can someone please help me.
Thanks in advance.

 

[Mooosie]

I think that you need to update your NPC libs.