DotNet HitTest BadFormat

How do I call a HitTest from a DotNet project?

I'm just trying the DotNet application SDK samples such as Gestures.

I'm guessing you would call a DotNet hit-test like this...

var hitTest = newHitTestWrapper(200, 200);

var result = _dvlRenderer.HitTest(hitTest);

if (Result.OK == result)

{

     ....

}

...but I always get a result of Result.BadFormat, which implies to me that m_uSizeOfDVLHitTest does not hold the expected value in the underlying sDVLHitTest struct

I am using visual studio 2015, and framework 4.5 (also tried 4.5.2)