DDQ: Lookup stored proc doesn't return value

[Sonix]

I'm using a data driven query with a lookup query that calls the following stored procedure:

CREATE PROCEDURE sp_getnextid (
  @key CHAR(20), @next_id d_count OUTPUT )
AS
SELECT  @next_id  = (NEXT_NO+1) FROM NEXT_NO
WHERE NEXT_KEY =  @key
UPDATE NEXT_NO SET NEXT_NO = @next_id
WHERE NEXT_KEY =  @key

RETURN @next_id
GO

In the Lookup query section I make a call to the procedure as:

DECLARE @next d_count 
EXEC sp_GetNextID @key = 'ITEM_ID', @next_id = @next OUTPUT 
SELECT @next

and have tested this works in Query Analyser. So in my ActiveX transformation script I then call the lookup as:

Dim itemID
itemID = DTSLookups("getNextID").Execute()
' assign parameters for insert
DTSDestination("ITEM_ID") 	= itemID

but although the procedure runs fine (the NEXT_NO table gets updated) the assignment for ITEM_ID fails. Can anyone help. The message I get is:

...encountered an invalid date value for 'ITEM_ID' destination column.

Please help. Its driving me mad!