firstly, the COM plugin needs to be registered. It is fine to register using regasm. Secondly, the plugin information needs to be registered in Navisworks key. Please refer to the attachments. I think your problem may probably: you renamed the plugin.
you do not need to clean up the registry. Register the plugin again, windows will look for the key by the guid. If it finds, it will override the information (new location, new name etc). Hope this makes sense.