I saw something similar to this when I was developing a plug-in as well.

Basically, when you register an extenstion, Google will attempt to verify that your COM object can actually be loaded. So it will go through the motions of instanciating your object. If something goes wrong along the way, it will fail.

Mine was because of a registry error, and if I remember correctly, it was because of my TypeLib key had a typo in it. But I do all of the work by hand, I prefer not to use ATL/MFC/.NET to do any of this.

Ian