ShowProgress does not work

Good morning colleagues. I will appreciate help from you. I cannot display a process warning message while an Ajax is running. I send you the code where ShowProgress does not work.
Regards.

      NSB.ShowProgress("Aguarde, enviando imagen...")

      req = Ajax("http://"+ccServidor+"/ScanDocManager/upload_imagen4.php", "POST", "file=" + fileName + "&content=" + fileContent + "&usu=" + cod_usu, Enviar_Imagen )
  
End Function

Function Enviar_Imagen()
    
    NSB.ShowProgress(False)
    
    If req.readyState <> 4 Then Exit Function 'ignore progress reports
    If req.status = 200 Then 'success
      TextResponse.value=req.responseText
    Else 'failure
      msg = "Error: Status = " & req2.status
      If TypeName(req.statusText)="string" Then msg = msg & " " & req.statusText
      If TypeName(req.err)="string" Then msg = msg & " " & req.error
      TextResponse.value=msg
    End If

End Function