New Post: MessageBox only opens once

I resolved it. It seems to be related to the fact that my main window is winforms and the rest hosted with elementhost. I noticed that it was not just your messagebox that had a problem opening more than once, it was other wpf windows opened from a hosted usercontrol also. The solution HERE solved it.

Basically you need to put the below code for the mainform Load event.

if (System.Windows.Application.Current == null) 
{ 
    new System.Windows.Application { ShutdownMode = ShutdownMode.OnExplicitShutdown }; 
}

And then for the in the ForClosed event

Application.Current.Shutdown()