<STAThread()> _
Shared Sub Main(args() As String)
    Dim App As Anwendung = New Anwendung
    App.ApplicationContext.MainForm = New frmStart
    App.Run(args)
End Sub
 
Class Anwendung
    Inherits WindowsFormsApplicationBase
 
    Public Sub New()
        Me.IsSingleInstance = True
        Me.EnableVisualStyles = True
    End Sub
 
    Protected Overrides Sub OnStartupNextInstance(eventArgs As _
      Microsoft.VisualBasic.ApplicationServices.StartupNextInstanceEventArgs)
        MyBase.OnStartupNextInstance(eventArgs)
        MsgBox("Diese Anwendung lässt sich nur einmal starten!")
        eventArgs.BringToForeground = True
    End Sub
 
End Class