AutoCAD .NET :: Double Click On Stretch Grip Of Dynamic Block Generate Fatal Error

I have this double click class. which works fine. In order  to clear grips after user finishes with double clicking,I  added  two lines (which shown on code below).  But having those two line make code faulty. When ?

if user select a dynamic block with stretch grip on it, then double click on stretch grip trianlge. code geneaarte fatal error. Funny thing is code doesn't catch. it. Is there any other way to clear grips after double click ?

Here is code:

Imports Autodesk.AutoCAD.RuntimeImports Autodesk.AutoCAD.ApplicationServicesImports Autodesk.AutoCAD.EditorInputImports Autodesk.AutoCAD.DatabaseServicesPublic Class Main_0_Class Implements IExtensionApplication Public Sub Initialize() Implements IExtensionApplication.Initialize dblClickEven_Class.Start() End Sub
[Code] .....