CreateProcessAsUser: Unhandled Exception

I couldn’t get this to work for me, I’m new to C# so maybe I’m doing something wrong, here’s the code

using System;
using murrayju.ProcessExtensions;

namespace spawnproc
{
    class Program
    {
        static void Main()
        {
            Console.WriteLine("Starting calc.exe");
            ProcessExtensions.StartProcessAsCurrentUser("calc.exe");
        }
    }
}

trying to run this will return the following error, with exit status code 255

Unhandled Exception: System.Exception: StartProcessAsCurrentUser: CreateProcessAsUser failed.

   at murrayju.ProcessExtensions.ProcessExtensions.StartProcessAsCurrentUser(String appPath, String cmdLine, String workDir, Boolean visible)
   at spawnproc.Program.Main()