2.2.1.1.2.4 MS-ASProtocolVersion
The MS-ASProtocolVersion header indicates the protocol version that the client is using to format the request. This header SHOULD NOT be used if the base64 encoded query value is being used. Instead, the Protocol version field of the base64 encoded query value SHOULD be set, as specified in section 2.2.1.1.1.1.
Valid values for this header are "14.1", "14.0", and "12.1".