C#

<br />
using System;<br />
using System.Windows.Forms.Design;<br />
<br />
namespace CusControl<br />
{<br />
public class MyControl:ScrollableControlDesigner<br />
	{<br />
	public MyControl()<br />
	{<br />
	}<br />
	<br />
protected override void PreFilterProperties(System.Collections.IDictionary properties)<br />
		{<br />
// TODO:  Add MyControl.PreFilterProperties implementation<br />
			properties.Remove("BorderStyle");<br />
//This will remove the property from base.<br />
	}<br />
	}<br />
}<br />
<br />

<br />
System.Diagnostics.Process.Start("C:\\windows");<br />

cmb.Items.Add("Option 1");
cmb.Items.Add("Option 2");
cmb.Items.Add("Option 3");
cmb.Items.Add(" ");
cmb.Items.Add("Option 4");
cmb.Items.Add("Option 5");

// Then, on your OK button handler

// Check for a separator being selected
// (I think it's something like this, but you get
// the idea)
if((string) cmb.SelectedItem == " ")
{
    MessageBox.Show("Select a valid option.");
    return;
}

// Close the dialog box if valid oprion selected
DialogResult = DialogResult.OK;