Emit(xmpp chat) connection Error:5920#0: *52 upstream timed out (110: Connection timed out) while connecting to upstream,

I tried to run emit(a gwt implemention of xmpp client) with ejabberd,and it works fine. I noticed that the developers of emit use a java servlet to proxy request to ejabberd:

  https://github.com/EmiteGWT/hablar/blob/master/src/main/java/de/spieleck/servlets/ProxyServlet.java),  

And I want to bypass this proxy,so I follow this post:

  http://anders.conbere.org/blog/2011/05/03/get_xmpp_-_bosh_working_with_ejabberd_firefox_and_strophe/  

But javascript client(complied from emit) takes long time to connect to ejabbered,and then disconnect quickly,and the nginx error log like this:

  2012/10/06 17:04:33 [error] 5920#0: *52 upstream timed out (110: Connection timed out) while connecting to upstream, client: 127.0.0.1, server: localhost, request: "POST /http-bind HTTP/1.1",   upstream: "http://111.186.4.11:5280/http-bind", host: "127.0.0.1", referrer: "http://127.0.0.1/hablartest/HablarTest1.html"  

Can anybody tell me what I did wrong?

My configuration: firefox-13 ejabberd-2.1.11 nginx-1.0.5 ubuntu-11.10

(since same client code(js code complied from gwt) with servlent proxy works fine,so I think it may be a nginx configuration problem)