You really should be using the PK from the Warehouse table (WarehouseID?)
linked to the Product table by WarehouseID (the FK).

For example, If you have two tables: Product and Warehouse, the SQL for the
subform would look like:  

(this is air code!!!)

SELECT Warehouse.WarehouseDesc
FROM Warehouse INNER JOIN Product ON Warehouse.WarehouseID_PK =
Product.WarehouseID_FK
WHERE Product.WarehouseID_FK = [forms]![Add an Order and Details].[combo102];

The SQL for Combo102 would be:

Select WarehouseID_PK, WarehouseDesc From Warehouse Order By WarehouseDesc;

And the after update event of Combo102 would be:

Sub Combo102_AfterUpdate()
 Me.[Order Details Subform].Requery
End Sub

NOTE  : Combo102 is unbound and in the form header.

I don't know your form design, how the subform relates to the main form, so
this probably won't work. But it should give you an idea on how to proceed.

HTH