C# NullReferenceException Error

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace Prototype
{
    public partial class Form1 : Form
    {
        object oDocument;
        int thmbNailCnt = 0;
        GroupBox[] thmbNail = new GroupBox[100];
        PictureBox[] picBox = new PictureBox[100];
        TextBox[] texBox = new TextBox[100];

        public Form1()
        {
            InitializeComponent();            
        }

        private void addWordToolStripMenuItem_Click(object sender, EventArgs e)
        {

        }

        private void scheduleToolStripMenuItem_Click(object sender, EventArgs e)
        {

        }

        private void label1_Click(object sender, EventArgs e)
        {

        }

        private void label2_Click(object sender, EventArgs e)
        {

        }

        private void label3_Click(object sender, EventArgs e)
        {

        }

        private void button9_Click(object sender, EventArgs e)
        {
            openFileDialog1.Filter = "Office Documents " + " " + "(*.doc, *.docx)|*.doc;*.docx";
            openFileDialog1.FilterIndex = 1;
            System.Windows.Forms.HtmlDocument document;
            string sFileName;
            openFileDialog1.FileName = "";
            openFileDialog1.ShowDialog();
            sFileName = openFileDialog1.FileName;

            if (sFileName.Length != 0)
            {
                oDocument = null;
                webBrowser1.Navigate(sFileName);
                document = webBrowser1.Document;
                newThumbNail(1, sFileName);
            }
        }

        private void webBrowser1_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
        {
            oDocument = webBrowser1.Document;

        }

        private void button8_Click(object sender, EventArgs e)
        {
            openFileDialog1.Filter = "Office Documents " + " " + "(*.xls, *.xlsx)|*.xls;*.xlsx";
            openFileDialog1.FilterIndex = 1;
            System.Windows.Forms.HtmlDocument document;
            string sFileName;
            openFileDialog1.FileName = "";
            openFileDialog1.ShowDialog();
            sFileName = openFileDialog1.FileName;

            if (sFileName.Length != 0)
            {
                oDocument = null;
                webBrowser1.Navigate(sFileName);
                document = webBrowser1.Document;

            }
        }

        private void button7_Click(object sender, EventArgs e)
        {
            openFileDialog1.Filter = "Office Documents " + " " + "(*.ppt, *.pptx)|*.ppt;*.pptx";
            openFileDialog1.FilterIndex = 1;
            System.Windows.Forms.HtmlDocument document;
            string sFileName;
            openFileDialog1.FileName = "";
            openFileDialog1.ShowDialog();
            sFileName = openFileDialog1.FileName;

            if (sFileName.Length != 0)
            {
                oDocument = null;
                webBrowser1.Navigate(sFileName);
                document = webBrowser1.Document;

            }
        }

        private void button10_Click(object sender, EventArgs e)
        {
            openFileDialog1.Filter = "Office Documents " + " " + "(*.pdf)|*.pdf";
            openFileDialog1.FilterIndex = 1;
            System.Windows.Forms.HtmlDocument document;
            string sFileName;
            openFileDialog1.FileName = "";
            openFileDialog1.ShowDialog();
            sFileName = openFileDialog1.FileName;

            if (sFileName.Length != 0)
            {
                oDocument = null;
                webBrowser1.Navigate(sFileName);
                document = webBrowser1.Document;

            }
        }

        private void newThumbNail(int docType, string fileName)
        {




            thmbNail[thmbNailCnt].Visible = true;            
            thmbNail[thmbNailCnt].Location = new Point(2, 5);
            thmbNail[thmbNailCnt].Size = new Size(222, 50);


            picBox[thmbNailCnt].Parent = thmbNail[thmbNailCnt];
            picBox[thmbNailCnt].Visible = true;
            picBox[thmbNailCnt].Location = new Point(6, 13);
            picBox[thmbNailCnt].Size = new Size(31, 31);
            picBox[thmbNailCnt].Image = new Bitmap("images/excel.png");

            texBox[thmbNailCnt].Parent = thmbNail[thmbNailCnt];
            texBox[thmbNailCnt].Visible = true;
            texBox[thmbNailCnt].Location = new Point(53, 24);
            texBox[thmbNailCnt].Size = new Size(163, 20);
            texBox[thmbNailCnt].Text = fileName;
            texBox[thmbNailCnt].Enabled = false;

            this.Controls.Add(thmbNail[thmbNailCnt]);
            this.Controls.Add(picBox[thmbNailCnt]);
            this.Controls.Add(texBox[thmbNailCnt]);


        }

        private void Form1_Load(object sender, EventArgs e)
        {

        }



    }
}

Моя программа выдает ошибку нулевой ссылки всякий раз, когда она входит в функцию private void newThumbNail(int docType, string fileName). Пожалуйста помоги. Я считаю, что правильно объявил groupBox, textBox и picture Box. Но я не уверен, что объявил допустимый массив groupBox.