private void SpreadsheetElement_MessageShowing(object sender, Telerik.WinForms.Controls.Spreadsheet.MessageShowingEventArgs e)
{
    e.IsHandled = true;
}

See the end of this message for details on invoking 
just-in-time (JIT) debugging instead of this dialog box.

************** Exception Text **************
System.ArgumentNullException: Value cannot be null.
Parameter name: text
   at System.Windows.Forms.Clipboard.SetText(String text, TextDataFormat format)
   at System.Windows.Forms.Clipboard.SetText(String text)
   at Telerik.WinForms.Controls.Spreadsheet.Clipboards.ClipboardEx.MSClipboardSetText(String text)
   at Telerik.WinForms.Controls.Spreadsheet.Clipboards.ClipboardEx.SetTextInternal(String text)
   at Telerik.WinForms.Controls.Spreadsheet.Clipboards.ClipboardEx.SetDataInternal(String text, WorksheetFragment fragment)
   at Telerik.WinForms.Controls.Spreadsheet.Worksheets.RadWorksheetEditor.Copy()
   at Telerik.WinForms.Controls.Spreadsheet.Worksheets.RadWorksheetEditorCommands.<>c.<InitializeCommands>b__575_94(RadWorksheetEditor editor, Object parameter)
   at Telerik.WinForms.Controls.Spreadsheet.Commands.RadSheetEditorDelegateCommand`1.ExecuteOverride(Object parameter)
   at Telerik.WinForms.Controls.Spreadsheet.Commands.RadSheetEditorCommandBase`1.Execute(Object parameter)
   at Telerik.WinControls.UI.RadSpreadsheetElement.<CreateDefaultWorkbookContextMenu>b__184_1(Object <p0>, EventArgs <p1>)
   at Telerik.WinControls.RadElement.OnClick(EventArgs e)
   at Telerik.WinControls.UI.RadButtonItem.OnClick(EventArgs e)
   at Telerik.WinControls.UI.RadMenuItem.OnClick(EventArgs e)
   at Telerik.WinControls.RadElement.DoClick(EventArgs e)
   at Telerik.WinControls.RadElement.RaiseBubbleEvent(RadElement sender, RoutedEventArgs args)
   at Telerik.WinControls.RadItem.RaiseBubbleEvent(RadElement sender, RoutedEventArgs args)
   at Telerik.WinControls.RadElement.RaiseRoutedEvent(RadElement sender, RoutedEventArgs args)
   at Telerik.WinControls.RadElement.DoMouseUp(MouseEventArgs e)
   at Telerik.WinControls.ComponentInputBehavior.OnMouseUp(MouseEventArgs e)
   at Telerik.WinControls.RadControl.OnMouseUp(MouseEventArgs e)
   at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
   at System.Windows.Forms.Control.WndProc(Message& m)
   at System.Windows.Forms.ScrollableControl.WndProc(Message& m)
   at Telerik.WinControls.RadControl.WndProc(Message& m)
   at Telerik.WinControls.UI.RadPopupControlBase.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.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

public Form1()
        {
            InitializeComponent();

            Workbook workbook = new Workbook();
            radSpreadsheet1.Workbook = workbook;

            Worksheet worksheet = workbook.ActiveWorksheet;

            CellStyle style = workbook.Styles.Add("HeaderStyle");
            style.IsBold = true;


            worksheet.Cells[0, 0].SetValue("first\ncell");
            worksheet.Cells[0, 1].SetValue("second cell");

            worksheet.Cells[0, 0, 0, 1].SetStyleName("HeaderStyle");
        }