I'm using table values for the first time as a parameter to a function in SQL Server 2008. The code below produces this error:

Must declare the scalar variable "@RESULT".

Why?! I'm declaring it on the first line of the function!

        ALTER FUNCTION f_Get_Total_Amount_Due(

      @CUSTOMER_LIST   [tpCSFM_CUSTOMER_SET_FOR_MONEY] READONLY

    )
    RETURNS [tpCSFM_CUSTOMER_SET_FOR_MONEY]
    AS
    BEGIN


 --Prepare the return value, start with initial customer list
 DECLARE @RESULT AS [tpCSFM_CUSTOMER_SET_FOR_MONEY]
 INSERT INTO @RESULT SELECT * FROM @CUSTOMER_LIST

 --Todo: populate with real values
 UPDATE @RESULT SET tpCSAM_MONEY_VALUE = 100

 --return total amounts as currency
 RETURN @RESULT

 END