I setup an upstream configuration with only one server for now, i will add a new one in a while.

im experiencing a strange error now and then when users are uploading files to a form they get sometimes in the browser ERROR 502 bad gateway
and on nginx error logs i get
[code]

2011/01/10 08:07:31 [error] 28135#0: *606977 upstream timed out (110: Connection timed out) while reading response header from upstream, client: XXX.XXX.XXX.XXX, server: , request: "POST /UserDetails.aspx?CultureId=1 HTTP/1.1", upstream: "http://backend1:80//UserDetails.aspx?CultureId=1", host: "host.host.com", referrer: "http://host.host.com/UserDetails.aspx?CultureId=1"

2011/01/10 08:07:31 [error] 28135#0: *606977 no live upstreams while connecting to upstream, client: XXX.XXX.XXX.XXX, server: , request: "POST /UserDetails.aspx?CultureId=1 HTTP/1.1", upstream: "http://backend/UserDetails.aspx?CultureId=1", host: "host.host.com", referrer: "http://host.host.com/UserDetails.aspx?CultureId=1"
[/code]

now i dont know what is the exact issue, or the upload timeout or maybe DNS issues..could it be IPv6 dns resolving the problem?

When the users upload directly to the server they dont get any timeout or errors.

Thanks in advance