facing problem on firing checked change event of radiobutton..sometime it will fire but sometime not.

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ASP.NET

my code
<asp:RadioButton ID="rdograph" runat="server" GroupName="rdo1" Text="Summary in Graphs" CssClass="rdograph" Checked="true" AutoPostBack="true" OnCheckedChanged="rdograph_CheckedChanged"/>

protected void rdograph_CheckedChanged(object sender, EventArgs e)
  {
       if  (rdoresponse.Checked)
      {
          divres.Visible = true;
          
      }