I have a master page with a form element and the defaultbutton attribute set to a server-side ImageButton. On one of my pages I want to \"override\" the masterpage defaultbutto
You could try using the "DefaultButton" property of a Panel...
Place your button or whole page or div in asp:Panel
// start panel
asp:Panel ID="pnlOpsCallSummay" runat="server" DefaultButton="btnSearch"
............
//Controls of your requirement
..........
asp:Button ID="btnSearch" runat="server" Text="Search"
close the pannel
No need of Overriding the master page button