Hi,
Here is how I would do it.
Remove the cboPublication completely from the main form.
The main form for adding new publications lets you select the category and
sub-category for a new publication, and it will pass the value for
sub-category to the subform through the link master fields and link child
fields.
On the subform there needs to be a textbox to type in the name of the new
publication along with the other details of the new publication.

I assume you have tables like this:
a table for Category
a table for Subcategory
a table for Publication

If not please post details of your tables

Jeanette Cunningham

You could (but see below as to why you don't need to) open a form, bound to
the Publications table via the NotInList event procedure of the publications
combo box.  Here's some code which does this for adding a new city to a
Cities table:

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

   Dim ctrl As Control
   Dim strMessage As String
   
   Set ctrl = Me.ActiveControl
   strMessage = "Add " & NewData & " to list?"
   
   If MsgBox(strMessage, vbYesNo + vbQuestion) = vbYes Then
       DoCmd.OpenForm "frmCities", _
           DataMode:=acFormAdd, _
           WindowMode:=acDialog, _
           OpenArgs:=NewData
       ' ensure frmCities closed
       DoCmd.Close acForm, "frmCities"
       ' ensure city has been added
       If Not IsNull(DLookup("CityID", "Cities", "City = """ & _
           NewData & """")) Then
       Response = acDataErrAdded
       Else
           strMessage = NewData & " was not added to Cities table."
           MsgBox strMessage, vbInformation, "Warning"
           Response = acDataErrContinue
           ctrl.Undo
       End If
   Else
       Response = acDataErrContinue
       ctrl.Undo
   End If

End Sub

Then in the Open event procedure of the frmCities form goes this code:

Private Sub Form_Open(Cancel As Integer)

   If Not IsNull(Me.OpenArgs) Then
       Me.City.DefaultValue = """" & Me.OpenArgs & """"
   End If
   
End Sub

The city would correspond to your publication, so your bound publications
form would have a bound combo box to select the sub-category, in the same way
that my frmCities form has one to select the County in which the city is
located.  

HOWEVER! As in your case you've presumably already selected a sub-category
in the second combo box, however, you can omit opening the bound publications
form completely and insert the row directly into the table.  Here's code for
the NotInList event procedure, again for cities which does this:

   Dim cmd As ADODB.Command
   Dim ctrl As Control
   Dim strSQL As String, strMessage As String
   
   Set ctrl = Me.ActiveControl
   strMessage = "Add new city to list?"
   
   strSQL = "INSERT INTO Cities(City) VALUES(""" & _
           NewData & """)"
   
   Set cmd = New ADODB.Command
   cmd.ActiveConnection = CurrentProject.Connection
   cmd.CommandType = adCmdText
   
   If MsgBox(strMessage, vbYesNo + vbQuestion) = vbYes Then
       cmd.CommandText = strSQL
       cmd.Execute
       Response = acDataErrAdded
   Else
       Response = acDataErrContinue
       ctrl.Undo
   End If

   Set cmd = Nothing

You'd have to expand theSQL statement of course to include the sub-category.
The SQL statement would be built like this:

   strSQL = "INSERT INTO tblPublications(Publication, SubCategoryID)
VALUES(""" & _
           NewData & """," & Me.ComboSubCategory & ")"

This assumes that the PublicationID column is an autonumber whose value will
be inserted automatically by the system when the new row is inserted by the
above SQL statement.

Ken Sheridan
Stafford, England