Inside a modalpopupextender panel, you need to add and set the UseSubmitBehavior to false for the OK/Cancel controls to be enabled with postback to behave outside of the ajax control.

Example:

<asp:LinkButton ID="OkButton" runat="server" Text="Button Text" UseSubmitBehavior="false" PostBackUrl="product.aspx?id=3" />


You can also use OnClick in the button to perform an action outside of ajax with UseSubmitBehavior=”false”.

Allow page redirect from an asp:linkbutton in an Ajax ModalPopupExtender is a post from: WebPaws.com