I updated SL on my PowerBook at roughly 6PM EST, and was able to log in. When I launched Second Life this evening at about 10PM EST, I got another "you need to update" dialog, so I hit OK and it downloaded an update. However, now when I try to launch Second Life.app, I get a dialog saying "You cannot open the application "Second Life" because it is not supported on this architecture." The icon has changed from the usual SL hand to an SL hand with a circle and slash through it. The version number is listed as "Second Life version 1.7.4.6." See attached screen capture.
Hardware: PowerBook G4 1.67GHz, 2GB RAM, MacOS 10.4.3