Microsoft SSTP VPN returning HTTP 503

The possible cause of this error is when the hostname of the VPN server is not resolved by the forward proxy in-front of the VPN client. 0x800704D4 means The network connection was aborted by the local system.Possible solutions could be to check your proxy settings inside the Internet explorer. If the settings are correct, please ensure you are able to access other web sites (e.g. www.microsoft.com) using the browser. If that also works through, try accessing the URI which SSTP uses internally i.e. https://vpn_server_name/sra_{BA195980-CD49-458b-9E23-C84EE0ADCD75}/ - please replace vpn_server_name with actual VPN server name. If you see error “the website cannot be found” inside your browser, that validates the hostname resolution failure. If you know the IP address of VPN server, try connecting with that. Else contact your network administrator (who is responsible for managing the web proxy – most probably your ISP) – giving them the details of the problem (i.e. hostname resolution is failing for that particular hostname). Also if possible check the Event Logs of RRAS server