About.com states the "Http/1.1 service unavailable" message is a way of referring to the "503 service unavailable" message. This message means the website being visited is unavailable due to maintenance or site traffic.
About.com also states the "503 service unavailable message" is usually a result of problems on the website owner's end and is rarely caused by local factors. There are a few possible ways of fixing this error. The first option is to refresh the website, which is accomplished by pressing the refresh button located next to the address bar. The second option is to restart both the router and the computer, or other browsing device in use. If these options fail, contact the administrator of the website to notify them about the problem and return to the website at a later time.