If there is no master page tab, then you aren't using the recommend development approach of Portal Engine. I'd suggest reviewing it again and changing it to Portal mode. Ask any Kentico Partner around who has been developing with Kentico since version 1, there is no need to do straight ASPX development mode. Learn how to use Webparts, Page Templates, Page Layouts, Widgets, etc to your advantage and not have ASPX work against you. ASPX mode WILL make ALL your upgrade paths much more difficult and typically cause problems.