- You should not write IE extensions in Managed Code.
- You need to register your code in both 32bit and 64bit mode. IE will not load your extension if it is only registered in one bitness. To quote the article you linked:
In order to be EPM-compatible, Toolbars and BHOs must be available in 32bit and 64bit flavors, to avoid toolbars or other UI appearing and disappearing as you navigate between zones that run at different bitnesses.