Please see the ticket here http://www.telerik.com/account/support-tickets/view-ticket?threadid=1010098. I still need to support IE8 browsers. The removal of the frameBorder attribute from the iframe rendering causes layout issues in IE8. Adding a property to the RadPageView project to re-enable this behavior would fix this issue. It could be false by default in order to pass the cited validation tool. The developer would have to enable the property in order for the frameBorder attribute to be rendered as frameBorder="0".
Refer Support Id 1122136 ( https://www.telerik.com/account/support-tickets/view-ticket?threadid=1122136 ) for screen shots and explanation... Where we use the ShowBaseLine property in Horizontal Orientation, the same feature is not available when in Vertical Orientation