.PPS not working

When I get an email with a .pps file, it will not open and suggests that I go to file associations and set uo a new association because the one assigned is invalid. The file association with .pps files is 'Microsoft Power Point". If I save the .pps file in my documents and click on it , it will open using Microsoft Power point. What is happening?

This is what I do, it works. I use WLM.
Unable to Open .PPS attachments directly from Windows Mail or Windows Live Mail - The Winhelponline Blog

I use Thunderbird as my email client and comcast as my ISP. I did an experiment to use Open Source to be the association for PPS and it works fine. I;m going to stay with that for now. Thanks for you help and support.