I have no idea what that error message is. Have you tried our support desk at (800) 892-0449? Also have you tried accessing your site directly in Internet Explorer, i.e. https://projectpoint.buzzsaw.com/client/sitename (where sitename is the name of the site to which you were invited)?
I experienced the same problem installing the Buzzsaw 2008 client on my Vista computer. It seems that you have to de-install the old Buzzsaw client first. I didn't. so I cleaned up the registry of my computer removing all old Buzzsaw client entries including the file association. Then I visited the https://projectpoint.buzzsaw.com/sitename site and downloaded and installed the new Buzzsaw client. Problem fixed
Arie van Dalen