I was working with a web service today trying to resolve a bug in the HTTP Analyzer that resulted in a "Connection Refused" error coming back from the server. I spent ages trying to connect to the server in different ways using telnet and other WS testing tools. They all seemed to work; but I couldn't work out why a simple socket connection would fail just for JDeveloper.
It turned out that after much nashing of teeth that there was a problem with the SOAPAction header. It was being set to "null" rather than just "". So the connection was being refused for a faulty header rather than the socket not being set up. The confusion came because you get the same error code back from a proxy in both cases. At least in the case of this particular server. (It was not clear what technology they were using to host the services underneath)
Still fixed the analyzer, just glad it finally clicked as to what was going on.