Your app has entered a break state, but there is no code to show because all threads were executing external code (typically system or framework code)

Question

Visual Studio 2017 breaks in debug mode and displays the message:

Your app has entered a break state, but there is no code to show because all threa

Answer 1

I got this when I accidentally set the startup project to a class library instead of the end project (in this case, a WPF application).