NZEC in c# on BLOCKDRO

Got an issue with a NZEC error and I can’t see what’s wrong. It works fine on my machine with the test example

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
class Program
{
    static void Main(string[] args)
    {
        int cases = int.Parse(Console.ReadLine());

        for (int i = 0; i < cases; i++)
        {
            // read
            int[] gridDim = ReadIntArray();
            int[,] grid = new int[gridDim[0], gridDim[1]];
            int[] startPos = ReadIntArray();
            int[] endPos = ReadIntArray();
            startPos[0] -= 1;
            startPos[1] -= 1;
            endPos[0] -= 1;
            endPos[1] -= 1;

            for (int j = 0; j < gridDim[1]; j++)
            {
                int[] gridRow = ReadIntArray();
                for (int k = 0; k < gridDim[0]; k++)
                {
                    grid[j, k] = gridRow[k];
                }
            }
            
            Console.WriteLine(numPassed(grid,startPos,endPos));
        }
        return;
    }

    
    static int[] ReadIntArray()
    {
        string instring = System.Console.ReadLine();
        return instring.Split(' ').Select(s => Convert.ToInt32(s)).ToArray();
    }

    static int numPassed(int[,] grid, int[] curPos, int[] destPos)
    {
        // move is valid?
        if (curPos[0] < 0 || curPos[1] < 0) return 0;
        if (curPos[0] > grid.GetLength(0)-1 || curPos[1] > grid.GetLength(1)-1) return 0;
        if (grid[curPos[0], curPos[1]] == 0) return 0;
        
        // has passed?
        {
            int sum = 0;
            foreach (int i in grid) 
            {
                sum +=i;
                if (sum > 1) break;
            }
            if (sum == 1)
            {
                
                if (curPos.SequenceEqual(destPos)) 
                {return 1;}
                else
                {return 0;}
            }
        }
        // attempt move
        int[,] postMove = (int[,]) grid.Clone();
        // shrink height
        postMove[curPos[0],curPos[1]] -= 1;
        int passedCount = 0;
        passedCount += numPassed(postMove, new int[2] {curPos[0]+1,curPos[1]}, destPos);
        passedCount += numPassed(postMove, new int[2] {curPos[0]+2,curPos[1]}, destPos);
        passedCount += numPassed(postMove, new int[2] {curPos[0]-1,curPos[1]}, destPos);
        passedCount += numPassed(postMove, new int[2] {curPos[0]-2,curPos[1]}, destPos);
        passedCount += numPassed(postMove, new int[2] {curPos[0],curPos[1]+1}, destPos);
        passedCount += numPassed(postMove, new int[2] {curPos[0],curPos[1]+2}, destPos);
        passedCount += numPassed(postMove, new int[2] {curPos[0],curPos[1]-1}, destPos);
        passedCount += numPassed(postMove, new int[2] {curPos[0],curPos[1]-2}, destPos);
        
        return passedCount;
    }
}
}
//