505 HTTP Version not supported. The Server denies delivering data in this HTTP Version. Use this Tag if you encounter this error message.
There are currently two HTTP Versions in use: 1.0 and 1.1. They differ in various connection type elements (keep-alive, pipelining etc.). By default 1.1 is used and most Servers support both modes.
Sometimes this error is also produced if the client fails to send a (valid) HTTP Version.
This error is part of the negotiation phase of the connection and will be thrown before the server parses other data of the request.