Hi Wsilva,
Thank you for choosing Syncfusion Products.
The warning message occurs because of the code (DiagramWebControl1.EnableCallbacks = false) which you have used in .cs file. Here I have mentioned link for the sample code for UpdatePanel.Please refer it.
The UpdatePanel getting postback only when the DiagramWebControl1.EnableCallbacks property set to false.The warning message which you have mentioned do not affect the behavior of the application.
http://files.syncfusion.com/support/Diagram.Web/Forums/F84635/UpdatePanel.zipRegards,
Gowri