The RadButton control is not compatible with the AjaxToolkit's ConfirmButtonExtender
. This is caused by a conflict between the RadButton's client-side functionality, and the extender. The ConfirmButtonExtender
control is designed to add a client-side functionality to the existing standard ASP.NET button control, while the RadButton, like the rest of our RadControls for AJAX, already has a rich Client API that lets you achieve complicated tasks while avoiding unnecessary post-backs.
My suggestion is to check the following online demo, implementing a similar functionality: Button / Confirm Postback
the Telerik team