503 is an HTTP status code. It means "Service Unavailable." More specifically, "The server is currently unable to handle the request due to a temporary overloading or maintenance of the server."
Jason, you should ask your webmaster, whoever that may be, to look at Apache's access logs (likely in /var/log/httpd or /var/log/apache2) for 503 responses, and send you the time and dates. From there you can reason why.