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

OR

if you are getting “503 Service Temporarily Unavailable error”?

Go to root folder of the project and find maintenance.flag file and delete it.

Than, Go to var/ folder and delete cache folder.

Now refresh you’re page . hope fully you’re problem has been solved.

Guys If you want to set you’re maintenance page or other information regarding this visit..

http://www.magentocommerce.com/knowledge-base/entry/configuration-general-maintenance-mode