MonoTester error message although program works fine

Hi, I'm trying to complete the final code challenge of the C# Basics course. The task requires the program to print "Yay!" as many times as the number that is entered and to catch and pass Format Exceptions when the user enters something else than an integer.

My code works in Visual Studio and in my Workspace environment just as required in the task instructions, but when I press "Check work" after pasting the same code in the editor window, I get the following error message:

System.ArgumentNullException: Value cannot be null. Parameter name: String at System.Number.StringToNumber (System.String str, System.Globalization.NumberStyles options, System.Number+NumberBuffer& number, System.Globalization.NumberFormatInfo info, System.Boolean parseDecimal) [0x00054] in /builddir/build/BUILD/mono-4.8.0/mcs/class/referencesource/mscorlib/system/number.cs:1074 at System.Number.ParseInt32 (System.String s, System.Globalization.NumberStyles style, System.Globalization.NumberFormatInfo info) [0x00014] in /builddir/build/BUILD/mono-4.8.0/mcs/class/referencesource/mscorlib/system/number.cs:745 at System.Int32.Parse (System.String s) [0x00000] in /builddir/build/BUILD/mono-4.8.0/mcs/class/referencesource/mscorlib/system/int32.cs:120 at Treehouse.CodeChallenges.Program.Main () [0x00012] in <32a2be91c59b40c49ea6b902dd449240>:0 at MonoTester.Run () [0x00095] in MonoTester.cs:86 at MonoTester.Main (System.String[] args) [0x00013] in MonoTester.cs:28

I suspect that I may get this error message because I have two loops in my code instead of just one, but that's only what I'm guessing.

BR, Kimmo

PS. I posted an earlier message related to the same task and thanks to the replies I got, I was able to change the code a little bit (I added another loop), so that it know works perfectly in Visual Studio and in my Workspace environment. Thanks for the comments!

using System;

namespace Treehouse.CodeChallenges
{
    class Program
    {
        static void Main()
        {

            Console.Write("Enter the number of times to print \"Yay!\": ");

            while (true)
            {
                int counter = 0;
                string entry = Console.ReadLine();

                try
                {
                    while (true)
                    {
                        int number = int.Parse(entry);
                        counter = counter + 1;

                        if (counter > number)
                        {
                            break;
                        }
                        Console.WriteLine("Yay!");

                    }
                }

                catch (FormatException)
                {
                    Console.WriteLine("You must enter a whole number.");
                    continue;
                }
            }

        }
    }
}