Cannot open assembly 'Program.cs': File does not contain a valid CIL image.

        bool keepGoing = true;
        while(keepGoing)
        {
            // Prompt user for minutes exercised 
            Console.Write("Enter how many minutes you exercised or type \"quit\" to exit: ");
            string entry = Console.ReadLine();        

            if(entry == "quit")
            {
                keepGoing = false;
            }
            else
            {
                // Add minutes exercised to total 
                int minutes = int.Parse(entry);

                if(minutes <= 10)
                {
                    Console.WriteLine("Better than nothing, am I right?");
                }
                else if(minutes <= 30)
                {
                    Console.WriteLine("Way to go hot stuff!");
                }
                else if(minutes <= 60)
                {
                    Console.WriteLine("You must be a ninja warrior in training!");
                }
                else
                {        
                    Console.WriteLine("Okay, now you're just showing off!");
                }

                runningTotal = runningTotal + minutes;

                // Display total minutes exercised to the screen 
                Console.WriteLine("You've entered " + runningTotal + " minutes.");
            }
            // Repeat until user quits
        }

        Console.WriteLine("Goodbye");
    }
}