I think it is not applicable to my current setup. Though there could be some connection with the problem  you encountered, meaning my SPS portal could not locate some files (or maybe) needed by my web  part (hmmm, could be).
I tried downloading a third-party web part, deployed it using the wppackager tool, and it was successfully installed (though it is only a basic  web part  compared to the SSO web part I want to create, basically because a lot of configuration settings are needed , e.g. permission for the SingleSignonPermission namespace).
Are there anyone out there who have successfully implement SSO in SPS2K3?
I'm running out of options and solutions, can anybody give some suggestions? I really needed it.