Aceman, cut the guy some slack it's the weekend, did you think maybe load3d can't work on this over the weekend, it's also a long weekend in the states if that is where he's from.
load3d,
The main form should be bound to a table/query...let's say table1, your sub bound to table2...table2 should have it's own ID plus the FK (foreign Key) field (number type)...this FK needs to be linked in the form design ( as Aceman is indicating). Check the Form properties of the subform and make sure "Link Child Fields" & "Link Parent Fields" are filled in correctly...the PARENT is the Primary ID of Table1 and the Child will the the FK of TABLE2...NOT table2's Primary key.