Access2002 .ADP "Run-time error 2455" -- "You entered an expression that has an invalid reference to the property Form/Report"

There's an unbound main form: frmDelivery, and an unbound subform: frmdeliveryItems.

The subform has a Public Sub, "ConnectSubform" that does the necessary binding.  The call from the mainform looks like this:

Private Sub ClearFields()
    txtDeliveryID = ""
    txtDeliveryTime = Now()
    cmbEmployee = ""
    cmbSupplier = 0
    Forms![frmDelivery]![frmDeliveryItemsSubform].Form.ConnectSubForm 0
    txtDeliveryTime.SetFocus
End Sub

The name of the subform, and the name of the subform control on the main form are both:
frmDeliveryItemsSubform (name of control)
frmDeliveryItemsSubform (data: source object of control)

The Public routine in the subform looks like this:
Public Sub ConnectSubForm(intDeliveryId As Integer)
    Me.RecordSource = "spDeliveryItemsSubformRecordSource"
    Me.InputParameters = "@DeliveryID=" & intDeliveryId
    intDelivery = intDeliveryId
    Me.Requery
    Me.UniqueTable = "tblPurchaseOrderItems"
    On Error Resume Next
    Me.Recordset.MoveLast
    intItemNo = txtDeliveryItemNo
End Sub

It's this line that causes the error:
Forms![frmDelivery]![frmDeliveryItemsSubform].Form.ConnectSubForm 0

... silly thing is, this has been working for the last 4 years... it only just stopped.  Is it co-incidence that I just upgraded to Access 2002?  The ADP is still in Access 2000 format.

I'm about ready to kill... been bashing my head against the wall for a week over this, so any/all help will be fallen on with whimpering gratitude!