Deriving from wrapper class

[Wenyuan Rao]

I am an user of your vtk wrapper for .net c#.

I've tried to create my own subclass from one of the wrapper class (vtkLinearTransform). But I was kept getting an exception saying "can't downcast from a pointer to a native class".

public class myICP : vtk.vtkLinearTransform
{
   ...
}

that exception pops up every time I write:
myicp.GetMatrix();

Could anyone tell me what the problem is? And if possible, hot to get around this.

Thanks
Wenyuan Rao