Tabpanel Set visible false not working in ASP web page server side

Question

    <AjaxToolkit:tabpanel runat="server" id="nourl" headertext=" " width="90%" height="100px" visible="false" >
    <headertemplate>  
                New 
            </headertemplate>  
            <contenttemplate >  
            <table border="0" cellpadding="0" cellspacing="0" width="100%">
               <tr>
                <td align="center"  valign="middle">                        
                </td>
            </tr>
        </table>

            </contenttemplate>  
    </AjaxToolkit:TabPanel>

        </ajaxtoolkit:tabcontainer>

This is the aspx file code

In server side i set visible true this tab panel and then i set visible false in another button event it not hide the tab panel. How to solve this problem

try
{
   DataTable dtFeedurls = getDatatable();

   if (dtFeedurls.Rows.Count > 0)
   {
     foreach (DataRow dr in dtFeedurls.Rows)
      {
         AjaxControlToolkit.TabPanel tb = new AjaxControlToolkit.TabPanel();
         tb.ID = ("Tab" + dr["COLUMN_1"].ToString());
         tb.HeaderText  = dr["COLUMN_2"].ToString();
         tc.Tabs.Add(tb);

     }

    nourl.Visible = false;

   }
   else
   {
     nourl.Visible = true;                
   }

   tc.ActiveTabIndex = 0;
}
catch (Exception ex)
 {
   throw ex;
 }

This the server side code