If you have tried to upgrade a WordPress plugin or WordPress itself, and failed. You might have ended up with your blog only returning “Briefly unavailable for scheduled maintenance. Check back in a minute.” error message. The reason for this is that WordPress takes the blog down before running any upgrades, so the users wont get any nasty error messages. But in some rare cases, WordPress cant seem to turn itself back on afterwards.
The solution is to delete the file “.maintenance” in your WWW-folder/website root folder. Your blog will then again begin to work as it should.