If you are writing an HL7 client, be careful that you are actually connecting to an HL7 server. One problem we have seen was a customer thought they were connecting to a remote HL7 server but was in fact connecting to a web server running on the local machine. This was confusing because a web server will accept the HL7 message and generate an error response which an HL7 server will ignore. The web server will then break the TCP/IP connection.