We were unable to connect to your server.
When the http address is checked by our servers, we wait a standard 15 seconds for a response. If we do not detect a response, this error will be triggered.
Under normal circumstances, when an http hostname is requested (e.g. example.com typed into your browser), the request goes out to a DNS server and gets converted into an ip address.
Your request can fail in two ways. Either the hostname could not resolve into an ip or the address simply does not exist.
If the problem was due to your hostname not resolving into an IP Address, there will also be a HTTP DNS problem listed as well.