Text' threw an exception of type 'Microsoft.VisualStudio.Debugger.Runtime.CrossThreadMessagingException'

Thread.Sleep(100);
this.Invoke((MethodInvoker)delegate
{

    myTextBox.Text += strMessage + "\r\n";
});

using System;
using System.Threading;
using System.Windows.Forms;

namespace WindowsFormsApplication1
{
    // DPM: 03/23/13.  Building on John Simmons excellent comment above, here is one simple example using similar tools. 
    // Create a simple Form with a single textbox called myTextBox.
    // Use System Timer Thread to flash myTextBox contents.
    // Could used to alert the user the app. is running when a longer method is executing.
    // for example: loading a grid, preparing a report, getting a traceroute trace, etc.

    // Requires cross thread communication.
    // Use a delegate and an invoke statement to allow a method in the Form to change controls in the Form.  
    // C# does NOT allow cross thread access directly to controls!!!

    // You can't access controls created on other thread directly from a thread. 
    // You need to call a method of the main thread which will update controls for you. 

 
    // Add try/catch to debug/follow execution.
    // REF:http://msdn.microsoft.com/en-us/library/0b1bf3y3(v=vs.100).aspx
    // REF:http://www.codeproject.com/Questions/54201/Text-threw-an-exception-of-type-Microsoft-VisualSt
    public partial class frmMain : Form
    {
        public delegate void InvokeDelegate();              // Delegate for Cross thread access from timer thread to form thread.
        public System.Threading.Timer timer;                // Timer thread.

        public frmMain()
        {
            InitializeComponent();
            runTimer();                                     // Start Timer.
        }

        /// Create Timer Thread.
        /// REF:http://msdn.microsoft.com/en-us/library/saba8ksx(v=vs.100).aspx
        public void runTimer()
        {
            try
            {
                int timeout = Timeout.Infinite;
                int interval = 1000;
                TimerCallback callback = new TimerCallback(InvokeMethod);       // Method to call on each timer event.
                System.Threading.Timer timer = new System.Threading.Timer(callback, null, timeout, interval);
                timer.Change(0, 1000);                                          // Changes the start time and the interval between method invocations for a timer.
            }

            catch (Exception e)
            {
                MessageBox.Show("runTimer: " + e.ToString());
            }
        }

        /// Action for each timer event.
        /// NOTE: State Object needed for callback communication.
        public void InvokeMethod(Object state)
        {
            try
            {
                myTextBox.BeginInvoke(new InvokeDelegate(FlashBox));        // Set Form method to perform changes on Form.
            }

            catch (Exception e)
            {
                MessageBox.Show("InvokeMethod: " + e.ToString());
            }
        }

        /// Method to change Form controls.
        public void FlashBox()
        {
            try
            {
                myTextBox.Text = (string.IsNullOrEmpty(myTextBox.Text)) ? "Executed the given delegate" : string.Empty;
            }

            catch (Exception e)
            {
                MessageBox.Show("FlashBox: " + e.ToString());
            }
        }
    }
}