Access: "Data type mismatch in criteria expression" Issue

I am currently working on a report and I am trying to build a query that keeps giving me this error: "Data type mismatch in criteria expression" In my first query, I am calculating the difference between two dates to get a day until our ship leaves port (ex. 6/12/13 minus 6/10/13 = 2 Days) with each revenue booking. I then created another query to sum all the revenue by the day. However, when I try to run the query, I get this error. For some reason it doesn't like me grouping by this calculated field. Does anyone know how I can get around this? Any help would be greatly appreciated!

Here is the code for the initial query(Query_Capacity_Calc_Voy_1):

SELECT 
    Table_Capacity_Original.VOYAGE_REFERENCE, 
    Query_Capacity_Total_Voy.Service_No, 
    Query_Capacity_Total_Voy.Direction, 
    Query_Capacity_Total_Voy.Sub_Service_No, 
    Table_Capacity_Original.[Date Stamp], 
    DateSerial(Nz(Left([Voyage_ETD_Date],4),"19000101"), nz(Mid([Voyage_ETD_Date],5,2),"19000101"), nz(Right([Voyage_ETD_Date],2),"19000101")) AS ETD_Date, 
    [ETD_Date]-[Date Stamp] AS Day_1, 
    Table_Capacity_Original.Revenue
FROM Query_Capacity_Total_Voy 
INNER JOIN (Table_Capacity_Original 
    INNER JOIN [Voyage-Results] 
    ON (Table_Capacity_Original.VOYAGE_REFERENCE = [Voyage-Results].VOYAGE_REFERENCE) 
    AND (Table_Capacity_Original.DIRECTION = [Voyage-Results].DIRECTION) 
    AND (Table_Capacity_Original.SERVICE_NO = [Voyage-Results].SERVICE_NO)) 
ON (Query_Capacity_Total_Voy.Service_No = Table_Capacity_Original.SERVICE_NO) 
AND (Query_Capacity_Total_Voy.Direction = Table_Capacity_Original.DIRECTION) 
AND (Query_Capacity_Total_Voy.Sub_Service_No = Table_Capacity_Original.Sub_Service_No);

Here is the code for the summing query (Query_Capacity_Calc_Voy_2):

SELECT 
    Query_Capacity_Calc_Voy_1.Service_No, 
    Query_Capacity_Calc_Voy_1.Direction, 
    Query_Capacity_Calc_Voy_1.Sub_Service_No, 
    Query_Capacity_Calc_Voy_1.Day_1, 
    Sum(Query_Capacity_Calc_Voy_1.Revenue) AS SumOfRevenue
FROM Query_Capacity_Calc_Voy_1 
INNER JOIN Query_Capacity_Total_Voy 
ON (Query_Capacity_Calc_Voy_1.Service_No = Query_Capacity_Total_Voy.Service_No) 
AND (Query_Capacity_Calc_Voy_1.Direction = Query_Capacity_Total_Voy.Direction) 
AND (Query_Capacity_Calc_Voy_1.Sub_Service_No = Query_Capacity_Total_Voy.Sub_Service_No)
GROUP BY 
    Query_Capacity_Calc_Voy_1.Service_No, 
    Query_Capacity_Calc_Voy_1.Direction, 
    Query_Capacity_Calc_Voy_1.Sub_Service_No, 
    Query_Capacity_Calc_Voy_1.Day_1;