public struct Tile
        {
            public short DefaultPalette;

            public Surface Image;
            public Surface Image1x;
            public Surface Image2x;
            public Surface ImageFullSize;

            public byte[,] ColorData;

            public double scale;

            public Tile(Tile t)
            {
                this = t.Clone();
            }

            public Tile Clone()
            {
                Tile t = new Tile();

                t.DefaultPalette = this.DefaultPalette;
                t.Image = this.Image;
                t.Image1x = this.Image1x;
                t.Image2x = this.Image2x;
                t.ImageFullSize = this.ImageFullSize;
                t.ColorData = this.ColorData;
                t.scale = this.scale;

                return t;
            }
        }
...

        //The tile that is currently being edited.
        public static Tile curTile;

        //History stack for undo actions.
        public static Stack<Tile> tileUndoStack;

...

        public bool updateCurrentTile()
        {
            Color[,] TileColor = new Color[TileSize, TileSize];

            for (int i = 0; i < TileSize; i++)
            {
                for (int j = 0; j < TileSize; j++)
                {
                    try
                    {
                        byte color = curTile.ColorData[i, j];

                        TileColor[i, j] = Palettes[curPalette].colors;

                        <span class="cpp-comment">//curTile.ColorData[i, j] = color;</span>
                    }
                    <span class="cpp-keyword">catch</span> (Exception ex)
                    {
                        <span class="cpp-keyword">return</span> <span class="cpp-keyword">false</span>;
                    }
                }
            }

            curTile.Image.SetPixels(<span class="cpp-keyword">new</span> Point(<span class="cpp-number">0</span>, <span class="cpp-number">0</span>), TileColor);
            curTile.Image1x = curTile.Image.CreateScaledSurface(curTile.scale, <span class="cpp-keyword">false</span>);
            curTile.Image2x = curTile.Image.CreateScaledSurface(<span class="cpp-number">2</span>.<span class="cpp-number">0</span> * curTile.scale, <span class="cpp-keyword">false</span>);
            curTile.ImageFullSize = curTile.Image.CreateScaledSurface(<span class="cpp-number">10</span>.<span class="cpp-number">0</span> * curTile.scale, <span class="cpp-keyword">false</span>);

            <span class="cpp-keyword">return</span> <span class="cpp-keyword">true</span>;
        }


        <span class="cpp-comment">//Called when a mouse button is clicked over the SDL WinForm control</span>
        <span class="cpp-keyword">private</span> <span class="cpp-keyword">void</span> surfaceControl1_MouseDown(object sender, MouseEventArgs e)
        {

            <span class="cpp-keyword">if</span> (e.X &gt;= <span class="cpp-number">70</span> &amp;&amp; e.X &lt; <span class="cpp-number">390</span>)
            {
                <span class="cpp-keyword">if</span> (e.Y &gt;= <span class="cpp-number">70</span> &amp;&amp; e.Y &lt; <span class="cpp-number">390</span>)<span class="cpp-comment">//If the cursor is over the edit-able tile</span>
                {
                    tileUndoStack.Push(curTile);<span class="cpp-comment">//Make's a history state</span>

                    <span class="cpp-keyword">int</span> x = (<span class="cpp-keyword">int</span>)(Math.Floor(((e.X - <span class="cpp-number">70</span>) / <span class="cpp-number">10</span>.<span class="cpp-number">0</span>) / curTile.scale));
                    <span class="cpp-keyword">int</span> y = (<span class="cpp-keyword">int</span>)(Math.Floor(((e.Y - <span class="cpp-number">70</span>) / <span class="cpp-number">10</span>.<span class="cpp-number">0</span>) / curTile.scale));

                    <span class="cpp-keyword">if</span> (e.Button == MouseButtons.Left)
                    {
                        <span class="cpp-keyword">if</span> (curTile.ColorData[x, y] != curColor[<span class="cpp-number">0</span>])
                        {
                            curTile.ColorData[x, y] = curColor[<span class="cpp-number">0</span>];<span class="cpp-comment">// Change that pixel's color to the currently selected color for the left mouse button</span>
                            updateCurrentTile();
                        }
                    }
                    <span class="cpp-keyword">else</span> <span class="cpp-keyword">if</span> (e.Button == MouseButtons.Right)
                    {
                        <span class="cpp-keyword">if</span> (curTile.ColorData[x, y] != curColor[<span class="cpp-number">1</span>])
                        {
                            curTile.ColorData[x, y] = curColor[<span class="cpp-number">1</span>];<span class="cpp-comment">// Change that pixel's color to the currently selected color for the right mouse button</span>
                            updateCurrentTile();
                        }
                    }
                }
            }
        }


        <span class="cpp-comment">//Called when the user click the undo button</span>
        <span class="cpp-keyword">private</span> <span class="cpp-keyword">void</span> undoToolStripMenuItem_Click(object sender, EventArgs e)
        {
            <span class="cpp-keyword">if</span> (Mode == EditorMode.Tile)
            {
                <span class="cpp-keyword">if</span> (tileUndoStack.Count &gt; <span class="cpp-number">0</span>)
                {
                    <span class="cpp-keyword">int</span> index = tileUndoStack.Count - <span class="cpp-number">1</span>;

                    curTile = tileUndoStack.Pop();

                    updateCurrentTile();

                    <span class="cpp-keyword">if</span> (tileUndoStack.Count == <span class="cpp-number">0</span>)
                    {
                        Action enableAction = delegate() { undoToolStripMenuItem.Enabled = <span class="cpp-keyword">false</span>; };
                        <span class="cpp-keyword">this</span>.BeginInvoke(enableAction);

                    }
                }
            }
        }


</pre></div><!–ENDSCRIPT–>

I've found that the problem <i>seems</i> to be occuring when updateCurrentTile is called in undoToolStripMenuItem_Click().

Thanks in advance for any help!