Hey I was using 2.5 and finally made the upgrade to 3.1.1. I follow WP's guide to safely upgrading (http://codex.wordpress.org/Upgrading_WordPress_Extended).
Afterward, everything seemed great, until I went to visit a post. It says that page doesn't exist. Here's an example:
The requested URL /blog/is-the-government-getting-coordinated-on-homeowners-in-foreclosures/ was not found on this server.
Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.
I've tried changing themes. I've tried changing the permalink naming structure. I've tried updating the post. Nada.