private ScriptManager _AjaxManager; 

/// <summary>
/// Oninit fires before page load. Modifications to the page that are necessary to support Ajax are done here.
/// </summary>
//protected override void OnInit(EventArgs e)
protected void AAA()
{
  _AjaxManager = ScriptManager.GetCurrent(this.Page);

  if (_AjaxManager == null)
  {
    //create new ScriptManager and EnablePartialRendering
    _AjaxManager = new ScriptManager();
    _AjaxManager.EnablePartialRendering = true;

    // Fix problem with postbacks and form actions (DevDiv 55525)
    Page.ClientScript.RegisterStartupScript(this.GetType(), this.ID, "_spOriginalFormAction = document.forms[0].action;", true);
          
    if (this.Page.Form != null)
    {
      string formOnSubmitAtt = this.Page.Form.Attributes["onsubmit"];
      if (!string.IsNullOrEmpty(formOnSubmitAtt) && formOnSubmitAtt == "return _spFormOnSubmitWrapper();")
        this.Page.Form.Attributes["onsubmit"] = "_spFormOnSubmitWrapper();";

        this.Page.Form.Controls.AddAt(0, _AjaxManager);
    }
  }
}

protected override void CreateChildControls()
{
  if (this.Field != null && this.ControlMode != SPControlMode.Display)
  {
    base.CreateChildControls();
    AAA();

    if (!this.Page.IsPostBack)
    {
      if (this.ControlMode == SPControlMode.New)
      {
      }
    }
  }
}