C#

Delegate: 
private delegate void ChangeTextDelegate(string text);

Method:
public static void ChangeText(string text)
        {
            if (richtextbox1.InvokeRequired)
            {
                richtextbox1.Invoke(new ChangeTextDelegate(ChangeText), new object[] { text });
            }
            else
            {
                int startIndex;
                startIndex = richtextbox1.TextLength; <- Exception points here
                ...
            }
        }

// Delegate:
private delegate void ChangeTextDelegate(string text);

// Method:
public static void ChangeText(string text)
{
    if (richtextbox1.InvokeRequired)
    {
        richtextbox1.Invoke(new ChangeTextDelegate(ChangeText), new object[] { text });
    }
    else
    {
        int startIndex;
        startIndex = richtextbox1.TextLength; // <- Exception points here.
        // ...
    }
}

// Delegate:
private delegate void ChangeTextDelegate(string text);

// Method:
public static void ChangeText(string text)
{
    if (<big><big>this</big></big>.InvokeRequired)
    {
        <big><big>this</big></big>.Invoke(new ChangeTextDelegate(ChangeText), new object[] { text });
    }
    else
    {
        int startIndex;
        startIndex = richtextbox1.TextLength; // <- Exception points here.
        // ...
    }
}

<pre lang="C#">// Delegate:
private delegate void ChangeTextDelegate(string text);

// Method:
public static void ChangeText(string text)
{
    if (<b><big><big><u>this</u></big></big></b>.InvokeRequired)
    {
        <b><big><big><u>this</u></big></big></b>.Invoke(new ChangeTextDelegate(ChangeText), new object[] { text });
    }
    else
    {
        int startIndex;
        startIndex = richtextbox1.TextLength; // &lt;- Exception points here.
        // ...
    }
}</pre>

System.InvalidOperationException was unhandled
  Message="Cross-thread operation not valid: Control 'SomeClass' accessed from a thread other than the thread it was created on."
  Source="System.Windows.Forms"
  StackTrace:
       at System.Windows.Forms.Control.get_Handle()
       at System.Windows.Forms.Control.get_InternalHandle()
       at System.Windows.Forms.Control.WmWindowPosChanged(Message& m)
       at System.Windows.Forms.Control.WndProc(Message& m)
       at System.Windows.Forms.TextBoxBase.WndProc(Message& m)
       at System.Windows.Forms.RichTextBox.WndProc(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
       at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
       at System.Windows.Forms.UnsafeNativeMethods.CallWindowProc(IntPtr wndProc, IntPtr hWnd, Int32 msg, IntPtr wParam, IntPtr lParam)
       at System.Windows.Forms.NativeWindow.DefWndProc(Message& m)
       at System.Windows.Forms.Control.DefWndProc(Message& m)
       at System.Windows.Forms.Control.WmCreate(Message& m)
       at System.Windows.Forms.Control.WndProc(Message& m)
       at System.Windows.Forms.TextBoxBase.WndProc(Message& m)
       at System.Windows.Forms.RichTextBox.WndProc(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
       at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
       at System.Windows.Forms.UnsafeNativeMethods.IntCreateWindowEx(Int32 dwExStyle, String lpszClassName, String lpszWindowName, Int32 style, Int32 x, Int32 y, Int32 width, Int32 height, HandleRef hWndParent, HandleRef hMenu, HandleRef hInst, Object pvParam)
       at System.Windows.Forms.UnsafeNativeMethods.CreateWindowEx(Int32 dwExStyle, String lpszClassName, String lpszWindowName, Int32 style, Int32 x, Int32 y, Int32 width, Int32 height, HandleRef hWndParent, HandleRef hMenu, HandleRef hInst, Object pvParam)
       at System.Windows.Forms.NativeWindow.CreateHandle(CreateParams cp)
       at System.Windows.Forms.Control.CreateHandle()
       at System.Windows.Forms.TextBoxBase.CreateHandle()
       at System.Windows.Forms.Control.get_Handle()
       at System.Windows.Forms.RichTextBox.get_TextLength()
       at SomeNamespace.SomeClass.Changetext(String text, Color color) in C:\...\SomeClass.cs:line 827
       at SomeNamespace.SomeClass.SomeThreadFun() in C:\...\SomeClass.cs:line 112
       at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.ThreadHelper.ThreadStart()
  InnerException: