Unable to cast mshtml.IHTMLDocument2 to IMarkupServices2 using mshtml Interop

Hi,

I am unable to cast mshtml.IHTMLDocument2 to IMarkupServices2 in C#. I am using Microsoft.mshtml Interop assembly (version 7.0).

The code snippet is

IHTMLDocument2 pdoc;

<pdoc assigned to a non-null value..............>

IMarkupServices2 markup = pdoc as IMarkupServices;

...> value of markup here is NULL even though pdoc is non-null and the msdn documentation indicate that IHTMLDocument2 can be used to get a reference to IMarkupServices2

To be more specific, i am able to get a non-null reference to IMarkupServices in case of a .Net Webbrowser control in a sample winforms application.

However when i try to get a similar reference to that of a running IE instance, i get NULL when i cast the non-null IHTMLDocument2 reference of the IE's browser control to IMarkupServices..

Is IMarkupServices inaccessible out of proc ..