about _RefPackitem table

well i'm writing my own query which it will help me to add custom items to the npc with the codename only !
so all works as far as i can feel it now
but i have a wired error shows if i tried to add another item ( the error cased by the Identity in _RefPackageitem)

my codes

Code:

if not exists ( select ID from _RefPackageItem where ID = 1 )
	SET @ID = '1'
if exists ( select ID from _RefPackageItem where ID = 1 )
	SET @ID = (SELECT TOP 1 ID FROM _RefObjCommon ORDER BY ID DESC )+1

it works fine for the first item !
but if i tried to add 2nd item it works fine but with a hecka high ID ! = [Only registered and activated users can see links. Click Here To Register...]
but if i tried to add the 3rd item i get this error !
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so i wonder which part made this error ?

----------------------Edit
already solved :D

Code:

if not exists ( select ID from _RefPackageItem where ID = 1 )
	SET @ID = '1'
if exists ( select ID from _RefPackageItem where ID = 1 )
	SET @ID = (SELECT TOP 1 ID FROM [B][COLOR="DarkRed"][COLOR="Red"]_RefObjCommon[/COLOR][/COLOR][/B] ORDER BY ID DESC )+1

it should be _RefPackageitem Not _RefObjCommon my bad sorry