Brian,
I recently experienced the exact same problem with my Lifestyle 35. Tried all the region code tricks mentioned above with no luck. Since purchasing my Lifestyle 35 in 2002, I have received 3 system update disks from Bose. Just to see what would happen, I tried reinstalling the updates, and checked to see if a store bought DVD would play after each update was installed. To my surprise, the system was restored to normal function after the second update was reinstalled. Store bought and copied DVDs now play normally. I have no idea why the fault happened, but I suspect that after you play a sufficient number of copied DVDs that have had the region code removed by the decrypting software, the Lifestyle 35 defaults to a no region code state and won't let you play region coded DVDs. Anyway, if you received the system update disks from Bose, give it a try and see what happens.
Steve