I have Omegle-clone chat service. In stress my nodejs (over 150 users) crash with error "TypeError: Cannot read property 'chId' of undefined" .

```
/home/kotka/randomi.fi/beta/varaserver2/channel.js:67
        f = this.channels[e].chId;
                      ^
TypeError: Cannot read property 'chId' of undefined
    at Channel.joinChannel (/home/kotka/randomi.fi/beta/varaserver2/channel.js:67:23)
    at Session.createSession (/home/kotka/randomi.fi/beta/varaserver2/session.js:21:23)
    at /home/kotka/randomi.fi/beta/varaserver2/path.js:1:268
    at Server.<anonymous> (/home/kotka/randomi.fi/beta/varaserver2/fu.js:43:3)
    at Server.emit (events.js:70:17)
    at HTTPParser.onIncoming (http.js:1610:12)
    at HTTPParser.parserOnHeadersComplete [as onHeadersComplete] (http.js:91:29)
    at Socket.ondata (http.js:1506:22)
    at TCP.onread (net.js:374:27)

```

What is problem and how I can fix it?

[channel.js source](http://pastebin.com/SnDUWrYi)