INSTEAD OF UPDATE trigger and cannot be a target of an UPDATE FROM statement

I have a view called Item

CREATE VIEW ITEM AS
SELECT * FROM General.DBO.ITEM
UNION
SELECT * FROM Specific.DBO.ITEM

Schema of Item & ItemLog in General & Specific
Itemcode int, ItemName varchar(50), Rate int, Flag char(1)
I have a trigger (Instead of Update) on this view :

CREATE TRIGGER UpdPageItem on Item
instead of update
as

Declare @Itemcode int, @ItemName varchar(50), @Rate int, @Flag char(1)

Select @Itemcode = Itemcode , @ItemName = ItemName, @Rate = Rate , @Flag = Flag from inserted

If @flag = 'G'

Insert General.DBO.ItemLog Values (@Itemcode , @ItemName , @Rate int, @Flag )

Else

Insert Specific.DBO.ItemLog Values (@Itemcode , @ItemName , @Rate int, @Flag )

Usually this table is updated with only one row!.

The above trigger works fine if i update with update .... set ....

If it is updated with the following, it raises the error!

INSTEAD OF UPDATE trigger and cannot be a target of an UPDATE FROM statement.

update Item set rate = (select rate from ....) where itemcode = @itemcode...

can u help me!?

I have to use update ..from only!?

Thanks in advance,