foreach (var reMod in re.Mods)
{
item.contents.itemList.Add(ItemManager.CreateByItemID(reMod));
}

After registering a weapon part, if you want to remove or move the part, this error occurs and you are kicked out. What is the problem?

Parts are equipped, but do not apply if you are holding a weapon. How should I fix it?

You could either use 

item.contents.AddItem(ItemDefinition itemToCreate, int amountToCreate);​

or you could do

Item attachment = ItemManager.CreateByItemID(reMod);

attachment.MoveToContainer(item.contents);

0x89A

You could either use 

item.contents.AddItem(ItemDefinition itemToCreate, int amountToCreate);​

or you could do

Item attachment = ItemManager.CreateByItemID(reMod);

attachment.MoveToContainer(item.contents);

thank you for telling me