title: Setting ComboBox SelectedIndex to 0 after adding items throws exception
body: <p>It's one of those days when even the simplest things don't work. TGIF. Consider the following code to populate a <code>combobox</code> which has been placed on a form using the designer:</p>
  
  <pre><code>   cboDisposition.Items.Add("Choose");  
     cboDisposition.Items.Add("Use as Is");  
     cboDisposition.Items.Add("Rework");  
     cboDisposition.Items.Add("Scrap");  
     cboDisposition.Items.Add("Return to Vendor");  
     cboDisposition.Items.Add("Void");  
     cboDisposition.DropDownStyle = ComboBoxStyle.DropDownList;
  
     cboDisposition.SelectedIndex = 0;
  </code></pre>
  
  <p>Setting the <code>SelectedIndex</code> causes an exception: <code>ex = {"Object reference not set to an instance of an object."}</code></p>
  
  <p>and the <code>SelectedIndex</code> is set to <code>-1</code>. Setting the value to any other <code>integer</code> between <code>1</code> and <code>5</code> works fine. Why is this happening?</p>
  
  <p>Thanks for any advice.</p>