Problem with Lowest Sums

Hello, I am getting an NZEC error when submitting my solution to the Lowest Sums problem under the easy category for the practice problems and I cannot understand why. Using both Visual Studio and MonoDevelop and testing under the .NET and gcms (Mono) compilers for C#, the program runs correctly and works fine. However, using Mono, I get an error after the program is finished running - which does not occur when running the .NET debugger. The error I get is: "Assertion at mono-threads-windows c:99 condition !mono_domain_get () not met" The program runs correctly, and then that error message comes up. Below is my code:

using System;

namespace Lowest_Sums
{
    class Program
    {
        static void Main(string[] args)
        {
            string s_cases = Console.ReadLine();
            int cases = int.Parse(s_cases);
            for (int k = 0; k < cases; k++)
            {
                string line1 = Console.ReadLine();
                string[] ln_split = line1.Split(' ');
                int chefs = int.Parse(ln_split[0]);
                int queries = int.Parse(ln_split[2]);
                int[] sums = new int[chefs * chefs];
                string s_satis = Console.ReadLine();
                string s_motiv = Console.ReadLine();
                string[] c_satisfaction = s_satis.Split(' ');
                string[] c_motivation = s_motiv.Split(' ');
                int curr_sum = 0;
                for (int i = 0; i < chefs; i++)
                {
                    for (int l = 0; l < chefs; l++)
                    {
                        int value1 = int.Parse(c_satisfaction[i]);
                        int value2 = int.Parse(c_motivation[l]);
                        sums[curr_sum] = (value1 + value2);
                        curr_sum++;
                    }
                }
                int[] sums_sorted = MergeSort(sums);
                for (int j = 0; j < queries; j++)
                {
                    string s_n = Console.ReadLine();
                    int n = int.Parse(s_n);
                    Console.WriteLine(sums_sorted[n - 1]);
                }
            }
        }

        static int[] MergeSort(int[] array)
        {
            if (array.Length == 1)
                return array;
            int[] sorted = new int[array.Length];
            int mid = (int)(array.Length / 2);
            int[] left = new int[mid];
            int[] right = new int[array.Length - mid];
            for (int p = 0; p < mid; p++)
                left[p] = array[p];
            int counter = 0;
            for (int p = mid; p < array.Length; p++)
            {
                right[counter] = array[p];
                counter++;
            }
            left = MergeSort(left);
            right = MergeSort(right);
            int leftptr = 0, rightptr = 0;
            for (int k = 0; k < left.Length + right.Length; k++)
            {
                if (leftptr == left.Length)
                {
                    sorted[k] = right[rightptr];
                    rightptr++;
                }
                else if (rightptr == right.Length)
                {
                    sorted[k] = left[leftptr];
                    leftptr++;
                }
                else if (left[leftptr] < right[rightptr])
                {
                    sorted[k] = left[leftptr];
                    leftptr++;
                }
                else
                {
                    sorted[k] = right[rightptr];
                    rightptr++;
                }
            }
            return sorted;
        }

    }
}

I'm using MergeSort to sort the final array. Thanks in advance.