Try to leave the socketfile and port parameters of the server2 configuration out and start the server, then grep for nsunix in the server log - at least in my case it generated a file in modules/nsunix. In the log entry it was something like this: "nsunix accepting "http://hostname.com:80/
"" which translated to a file named hostname.com.nsunix in modules/unix. Dont know what you are supposed to write in the proxy hosts's configuration though.
Also check that your webserver user has write access to that directory.