An HTTP client using an HTTP data stream to send data to the server is able to include specifications for the stream, known as Preconditions. If a precondition was specified, but not met, this error page will be generated by the server.
As this issue may only be generated when a client side application does not meet the specifications set by itself, this would need to be diagnosed as an issue with the client and identifying the precondition that is not being met.
