503 Service Temporarily Unavailable

I have installed a PHP photo album from here: http://www.maianscriptworld.co.uk/scripts_gallery.html

but whenener I try to update the options, I get this message:

"Service Temporarily Unavailable

The server is temporarily unable to service your request due to maintenance downtime or capacity problems. Please try again later."

Why isn’t the server updating the options and giving this message instead?