Error: connect EMFILE - not error due to too many open files

Getting following error in nodejs. I am sure its not error due to - Too many open files

I have thousand of client requests and using request.post into the code.

events.js:66
        throw arguments[1]; // Unhandled 'error' event
                       ^
Error: connect EMFILE
    at errnoException (net.js:768:11)
    at connect (net.js:644:19)
    at Socket.connect (net.js:709:9)
    at dns.js:71:18
    at process.startup.processNextTick.process._tickCallback (node.js:244:9)