Erro ShowDialog


Estou tendo um erro quando utilizo ShowDialog()

Showing a modal dialog box or form when the application is not running in UserInteractive mode is not a valid operation. Specify the ServiceNotification or DefaultDesktopOnly style to display a notification from a service application.

Line 42:         abrir.Filter = "Arquivos Textos (*.txt)|*.txt" 'filtar por arquivos txt
Line 43:         abrir.RestoreDirectory = True
Line 44:         abrir.ShowDialog() 'abre a janela de dialogo
Line 45:         arquivo = abrir.FileName 'nome do arquivo
Line 46:         Me.TxtArquivo.Text = abrir.FileName

Luis Carlos