Hi,
Thank you for your interest in Syncfusion Products.
We regret to let you know that the controls CallbackPanel and the CallbackMultiplexer are to be deprecated in the future releases. The CallbackPanel is marked obsolete, because we are on a migration to support ASP.NET AJAX framework with our ASP.NET controls. We would suggest you to use UpdatePanel class instead, which enables the sections of the page to be partially rendered without a postback.
Refer a simple sample with a GridGroupingControl and UpdatePanel.
http://files.syncfusion.com/support/GGC.Web/7.2.0.37/F84725/Sample.zipThanks,
Rekha