Access - CORREGIR CODIGO DE VALIDAR SI EXISTE UN CAMPO

Private Sub txtcurp_AfterUpdate()

Dim vValor, vValorB As String

vValor = Me.txtcurp.Text

If IsNull(vValor) Then Exit Sub

   vValorB = DLookup("[curp]", "Pacientes", "[curp]='" & vValor)

   If vValorB = vValor Then

       MsgBox "Ya existe un registro de este paciente", vbInformation, "AVISO"

        Me.txtcurp.Value = Null

        Me.ID.SetFocus

       Me.txtcurp.SetFocus

   End If

End Sub