It will remind you that the store is in "Maintenance Mode"... even you are logged in as administrator (Front and Back Ends).

For OpenCart 3+
Just go Extensions/Installer and in Extensions/Modifications "click the refresh button to rebuild your modification cache"

FOR 2.0.3.1
just copy content of upload folder to the root of your web site: it's just an image. and load ocmod file.
you can change the image if you want