title: why 'system.web.ui.scriptmanager' does not contain a definition for 'registerpostbackcontrol'?
body: <p>download button inside tabpanel doesnt work.. i try this method : </p>
  
  <pre><code>  ImageButton lb = e.Row.FindControl("ImageButton1") as ImageButton;  
              if(lb != null)
              ScriptManager.RegisterPostbackControl(lb);
              int index = ((GridViewRow)((ImageButton)e.CommandArgument).Parent.Parent).RowIndex;
  </code></pre>
  
  <p>but why it says 'system.web.ui.scriptmanager' does not contain a definition for 'registerpostbackcontrol' ? i already use system.web.ui on header... please help</p>