OK thanks. It seams like I have to make some kind of setting du to this error:
System.InvalidOperationException: It is invalid to show a modal dialog or form when the application is not running in UserInteractive mode. Specify the ServiceNotification or DefaultDesktopOnly style to display a notification from a service application.
at System.Windows.Forms.MessageBox.ShowCore(IWin32Window owner, String text, String caption, MessageBoxButtons buttons, MessageBoxIcon icon, MessageBoxDefaultButton defaultButton, MessageBoxOptions options)
at System.Windows.Forms.MessageBox.Show(String text)
Suggestions?