First:  I use an offline reader and expect to find the entire thread
in each post.  I won't participate in threads that require jumping
back and forth between discrete posts.

I'm not at all sure that we're all talking the same entities when we
talk about subforms and their content.  I never use a table in a
subform control.  Instead, I use a subform which is a form designed
such that the individual record is the heighth of just over a single
control. I display that form "continuous" within the subform control
in order to display many records.

It you are displaying a table in a subform control and have designed
Lookup Fields (combobox controls) into your tables, then I don't want
to play.  Look on www.mvps.org/access for the evils of Lookup Fields
in Tables.

It is the NotInList event of the combobox on the sub form you designed
that's in your subform control that should fire when the Author name
you've entered cannot be found in the list of Authors.  BTW it would
seem to me that if an Author ID were not found you'd want to alert the
user of a typo or other error but *not* offer to add a non-existent
ID.

Just found an old instance of NotInList.  Your mileage may vary so use
at your own risk....

Private Sub GetShopName_NotInList(NewData As String, Response As
Integer)

   On Error GoTo GetShopName_NotInList_error

   Dim strMsg As String
   Dim mydb As Database
   Dim rst As Recordset
   Dim CapStr As String

   strMsg = "'" & NewData & "' is not a listed shop.  "
   strMsg = strMsg & "Would you like to add it?"
   If MsgBox(strMsg, MB_YESNO, "New Job Shop") = IDNO Then
       SendKeys "{ESC}"
       Response = DATA_ERRCONTINUE
   Else
       Response = DATA_ERRADDED

       Set mydb = CurrentDb()
       Set rst = mydb.OpenRecordset("tblItem")
       rst.AddNew
           rst!Item = NewData
       rst.Update
       rst.Close
       mydb.Close

       DoCmd.OpenForm "frmAddShops", , , , A_ADD ', A_DIALOG
       Forms!frmAddShops.Caption = "Adding " & NewData
       Forms![frmAddShops]![Item].SetFocus
       Forms![frmAddShops]![Item].Text = NewData
       Forms![frmAddShops].Modal = True

   End If

Exit Sub

HTH