Nginx forward proxy - 502 bad gateway

I have install nginx forward proxy in two Ubuntu 12.04 servers with the
following configuration.

server {
listen 8080;

location / {
proxy_pass http://$http_host$uri$is_args$args;

After this I use the two servers as proxy on firefox.
The one server works fine.

But on the second server I get the message 502 bad gateway.

This server is behind a cisco firewall with port 8080 open. Where is the

The line:

proxy_pass http://$http_host$uri$is_args$args;

has problem with firewalls? or it is something else?

are you able to connect to $http_host from that second server,
maybe via lynx/w3m?
$ telnet $http_host 8080

and then


additionally, can you execute the following on that
server to check if you’re able to connect to your resolver:

$ nslookup $http_host

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