Dim boOrderExists As Boolean
boOrderExists = IIf(DCount("*", "[tblOrders]", "[OrderID]='" & Me.OrderID) = 0, False, True)
If boOrderExists Then
DoCmd.OpenForm "frmYourOrderForm", , , "[OrderID]=" & Me.OrderID
Else
DoCmd.OpenForm "frmYourOrderForm", , , , acFormAdd
End If