title: Invalid Cast Exception radbutton telerik (oncheckedchanged)
body: <p>I'm using a telerik Radbutton to act like a checkbox.
  However, when I click on the checkbox I receive a <code>A first chance exception of type 'System.InvalidCastException' occurred in Webapplicatie.dll</code></p>
  
  <p>See code below for asp.net code:</p>
  
  <pre><code>   &lt;telerik:RadButton ID="RadButton1" runat="server" Text="Hele dag" ToggleType="CheckBox" ButtonType="ToggleButton"  OnCheckedChanged="RadButton1_CheckedChanged"&gt;
                          &lt;/telerik:RadButton&gt;
  </code></pre>
  
  <p>and:</p>
  
  <pre><code>protected void RadButton1_CheckedChanged(object sender, EventArgs e)
          {
              try
              {
                  if (RadButton1.Checked)
                  {
                      lbStarttijd.Visible = false;
                      lbEindtijd.Visible = false;
  
                      rtp_Eindtijd.Visible = false;
                      rtp_Starttijd.Visible = false;
                      //rtp_Eindtijd.Enabled = false;
                      //rtp_Starttijd.Enabled = false;
                  }
                  else
                  {
                      lbStarttijd.Visible = true;
                      lbEindtijd.Visible = true;
                      //lbEindtijd.Enabled = true;
                      //lbStarttijd.Enabled = true;
                      rtp_Eindtijd.Visible = true;
                      rtp_Starttijd.Visible = true;
                      //rtp_Eindtijd.Enabled = true;
                      //rtp_Starttijd.Enabled = true;
                  }
              }
              catch (Exception ex)
              {
                  Debug.WriteLine(ex.Message + "\n" + ex.StackTrace);
              }
          }
  </code></pre>
  
  <p>However, the weirdest thing is, it does not end up in my Catch.
  I don't see why this is causing a invalid cast exception. Help appreciated :)</p>
  
  <p><strong>Side Note:</strong> This only happens when I 'bash' the checkbox by spam-clicking it.</p>