If you’ve logged in to your admin screen lately, you should have see a notice that “WordPress 2.8.5 is available! Please update now.” It’s not a major update. WordPress is calling it a “hardening” release; it’s basically a security update.
I updated plugins at the same time I updated to 2.8.5 on TechnoEarthMama, and All in One SEO Pack was one of those with an update. Some people have gotten 502 errors recently after updating this plugin; I got one when I tried to go to the plugin’s admin screen to update options. I simply deactivated and reactivated the plugin, and everything was fine after that, but if it’s still not working for you, Devin Price tweeted a post on the WordPress.org forums which offers another solution. It does require editing the plugin. Also, don’t forget that there’s a radio button you need to click on the All in One SEO Pack settings page to enable the plugin (in addition to activating the plugin through WordPress).