Trigger And Identity Column : What's Wrong ?

Hi,

I have to tables : Rank and Item
Rank contains a FK named R_I_id which references Item's primary key named I_id, which is also an identity column.

I want the field R_I_id of table Rank to be updated with the value of Item's I_id when a new Item is inserted. So I wrote the following trigger :

CREATE TRIGGER [dbo].[trg_oninsertitem]
ON [dbo].[Item]
AFTER INSERT
AS
BEGIN
SET NOCOUNT ON
SET IMPLICIT_TRANSACTIONS OFF
DECLARE @I_id INT
SELECT @I_id = SCOPE_IDENTITY()

BEGIN TRANSACTION
INSERT Rank(R_I_id) VALUES(@I_id)
IF (@@ERROR <> 0) BEGIN
PRINT 'error in trigger trg_oninsertitem'
ROLLBACK TRANSACTION
END
COMMIT
END

But when I insert a value in Item, I got the following message :

Msg 515, Level 16, State 2, Procedure trg_oninsertitem, Line 17
Cannot insert the value NULL into column 'R_T_id', table 'base.dbo.Rank'; column does not allow nulls. INSERT fails.

and I don't understand, because my trigger is fired after the value is inserted in table Item, so the field I_id should contain a new identity value, not NULL

my DBMS is SQL Server 2000

thanks in advance for your help