hello, i need Help

I have added a Qty Column in alias table, the Item have to many alias but the qty is different for each item style, I'm try to program a hook wich when the item is scanned the hook check based on alias if this item have a qty value if it's have a qty value more than 1 return the value stored in qty column to the pos grid, I have tryed using SetQuantityOnOrder  function but when the item is scanned POS say error can not load the dll, I have try with other function like example in customization guide and it works, how can i do this. thanks, and sorry for my english!.