Earlier this afternoon, I attempted to upgrade one of my WordPress blogs using the automated option, rather than copying all the files across manually (my usual approach). After about five minutes of inactivity, I assumed the process had completed and clicked on one of the links in the sidebar, only to receive a message about the site being in ‘maintenance mode’. I couldn’t access any pages on the site, nor could I get to the admin panel, and there was no obvious option in the database to switch off maintenance mode.
If this happens to you, the fix is to go into the root directory of your WordPress install and delete the file called ‘.maintenance’, then upgrade manually. You may need to edit the settings in your FTP client to see this file, as starting with a dot means it may be hidden from a standard listing. I also strongly recommend avoiding the automated upgrade feature until the developers have worked out a way for it to be reversed if anything goes wrong. Incidentally, the same advice applies to phpBB, as I encountered exactly the same problem when using its supposedly easy automated upgrade instead of manually copying the files myself.