I almost never use the WordPress Update system from directly within the WordPress admin panel to update a site or to update plugins. It just seems that more often than not something hangs and forces me to do it manually with FTP anyway.
But… I was trying to work quickly this afternoon and I decided to go ahead and use the WordPress update functions.
I clicked the update link and entered the site’s FTP credentials and pressed submit. At first it looked good, but it then quickly became apparant that the update was hanging and not going to complete correctly. At this point the site was a blank white page with the following text:
Briefly unavailable for scheduled maintenance. Check back in a minute.
Since the site appeared to hang during the update, I went ahead and fired up the FTP and transferred all the files over to the server to manually update WordPress. Unfortunately, this didn’t fix the problem! The site was stuck with the maintenance screen and I had no web access to the admin panel.
After poking around I found the problem. It looks like the .maintenance file didn’t get deleted when the update hung up.
Luckily, if you ever get stuck on the maintenance screen all you have to do is delete the .maintenance file in the root location of your website’s files using FTP. Once this file is removed, the site will no longer be locked out. If there is still a problem with your install, you should now at least see an error to tip you off.