Urgent - getting Invalid use of null

[Coleen]

If anyone can please help - I have an urgent need to find out why all of a
sudden a subform using the below SQL is now getting an invalid use of null
error:

SELECT DISTINCTROW Orders.OrderID, Orders.CustomerID, Orders.OrderDate,
Orders.FreightCharge, Orders.SalesTaxRate,
Sum(OrderDetailsExpanded.SumElements) AS LineTotal,
Sum(OrderDetailsExpanded.Cent) AS LineTotal1Cent, Orders.ShipDate,
Orders.PaymentAmount
FROM Orders LEFT JOIN OrderDetailsExpanded ON Orders.OrderID =
OrderDetailsExpanded.OrderID
GROUP BY Orders.OrderID, Orders.CustomerID, Orders.OrderDate,
Orders.FreightCharge, Orders.SalesTaxRate, Orders.ShipDate,
Orders.PaymentAmount;

I have recently made an entry to the Products table - but it is not even
used here. I was not getting this error before and now when I open the Main
form which has a subform using this SQL I get invalid use of null, and NO
records in the subform will display! I have not updated the SQL in any way,
so I don't know why it is not working. The Query OrderDetails Expanded
works fine on its own and the table Orders opens without errors.

Any help would be GREATLY appreciated.

Thanks.

Coleen