Plugin upgrade issue

How to clear the “Briefly unavailable for scheduled maintenance” message after doing automatic upgrade?

As part of the automatic upgrade
WordPress places a file named
.maintenance in the blog base
folder (folder that contains the
wp-admin folder). If that file exists,
then vistors will see the message
Briefly unavailable for scheduled maintenance. Check back in a minute.

To stop that message from being
displayed to vistors, just delete the
.maintenance file. The automatic
upgrade should be executed again, just
in case it failed.