If you are using WordPress’s automatic upgrade feature, you might occasionally run into the message “Briefly unavailable for scheduled maintenance. Check back in a minute.” Often, that message will remain even after the upgrade has been completed. This happened to me while I was testing out WP 3.0 RC3 today. After a long time of searching, I’ve figured out how to fix it.
Cause of the Message
During the upgrade processs, a “.maintenance” file is placed in the blog root directory to prevent visitors from seeing a broken blog during the upgrade. Although the feature is pretty handy, occasionally the message won’t go away after the upgrade. If the upgrade fails or is interrupted, nobody will be able to access the blog.
Fixing it is very simple. All you have to do is delete the .maintenance file from the blog root directory. After the file has been deleted, the site will begin working again.
Since the upgrade probably have failed, you might have to upgrade again. At this point, it’s probably a better idea to manually upgrade WP from FTP since it has failed from WP admin.
Possible Reasons for Error
There are many reasons for getting this error to begin with. First of all, many web hosts have disabled the feature to request remote files. Many hosts also have trouble extracting the ZIP file downloaded from WP.org. There can be lots of other causes, such as memory exhaustion, or a timeout.