AutoCAD .NET :: Create Paper Space Viewport And Show Some Model Portion In View

We like to allow user to select a rectagular area in modal scpace. Then the code creates a paperscace viewport in a spcified layout. The viewport will show the selected area. find the old VBA code that achived this and the .net code I am trying with. .Net code always gives some exception.

VBA Code

 'Lets find the center of the viewport in paperspace.

    Dim center(0 To 2) As Double
    center(0) = newWidth / 2
    center(1) = newLength / 2
    center(2) = 0
    Dim lay As AcadLayout
    For Each ent In ThisDrawing.layouts

[code].....