I have an iMac running OS X version 10.6.8 and had the same issue. I downloaded Second Life version 3.6.6.280963 and it locked up so I couldn't login. I finally trashed all my chat logs, preferences, the whole folder as a matter of fact. Then reinstalled from the DMG. As soon as I openerd it, it installed an "update" back to Second Life version 3.6.4.280048. Linden Labs has some explaining to do! I also hate losing my preferences as I'm on a limited bandwidth connection and all my pref's get set to medium with voice and video. All the things that cause lag and suck bandwidth. Sometimes I hate the Linden Labs viewer as much the other people I chat with!