I didn't use nmc in the past few weeks, and now it has stopped working.
Networker itself hasn't changed, although there were OS updates on both
client and server.

javaws gconsole.jnlp

results in the login window for an authorised user. After entering login
details, an "Application Error" window pops up with
 Security Exception
  java.net.MalformedURLException: unknown protol: socket

Selecting "Details", a java trace is shown. Clicking "ok", an error window
pops up with "Problem contacting server <server name>: Can't connect to SOCKS
proxy:Connection refused."

netstat shows that the networker httpd is listening on the server on port 9000.

I removed ~/.java and downgraded to jre 1.6.37, but no change. Baffling.

Server OS: CentOS 6.3 x86_64; networker 7.6sp4
Client: CentOS 5.9 x86_64
Java: Oracle jre 1.7.11 and 1.6.37