CS-Script is busy despite not running anything else?

Question

I'm running Visual Studio and CSScript. My program is extremely simple.

using System;
namespace HelloWorld
{
class Hello 
{
    static void Main() 
    {
        Console.WriteLine("Hello World!");

        // Keep the console window open in debug mode.
        Console.WriteLine("Press any key to exit.");
        Console.ReadKey();
    }
}
}

However, when I try to run it, the error message shows:

CS-Script is busy.

Edit: @TheGeneral mentioned that I forgot to include how I was running the program, which is a very valid concern. I am running the program using coderunner in Visual Studio.