Add a value to a combobox in Access Project Sql Server Backend

I am work with this script that I found on this site however I am getting an error at this point in the script.

Set RS = MyDataBase.OpenRecordset("dbo.Client")

I can get it to respond and open a msg/input box where I can add the the new item to Client_Name  (a text Field column two).  The combo box is bound to column one Client_ID(autonumber) and the table is Client.  What I need is for the person to be able to add a new item to this lookup table if it does not exist and choose that item.



The full script is


Private Sub Targeted_Customers_AfterUpdate()
Customer_ID_Update = Date

Dim ListData As String, Message As String
Dim MyDB As Database, RS As Recordset

If [Targeted_Customers].Column(1) = "<Add New Item>" Then

    Message = "Please Enter a New Item"    ' Set prompt.
    ' Display message
    ListData = InputBox(Message)

If Not IsNull(ListData) Then

Set MyDataBase = CurrentDb()
Set RS = MyDataBase.OpenRecordset("dbo.Client")

RS.AddNew
    RS("Client_Name") = ListData
RS.Update

RS.Close
Set RS = Nothing
db.Close
Set db = Nothing

End If

[Targeted_Customers].Requery  '<----Updates the list

End If




End Sub