SlidingPaneLayout in FragmentActivity can not be 'found'

Can someone help with this:

Below image illustrates the issue and saves me exlaining.

1) SlidingPaneLayout inside a FragmentActivity. 2) It works fine. 3) I can not get access to the instance of SlidingPaneLayout using (SlidingPaneLayout)FindViewById (Resource.Id.drawer_layout); as I get a cast exception. 4) The found object seems to be of the correct type. 5) What am I doing wrong?!

Thanks.