nginx in proxy mode, timeouts

[Juergen Gotteswinter]

Hello,

someone could give me a hint what this error messages should mean? e.g. 
if its something nginx related, client related or backend...


2009/08/17 12:22:48 [error] 22557#0: *1683003 upstream timed out (110: 
Connection timed out) while reading upstream, client: 82.207.xxxxxx, 
server: xxx.de, request: "POST /index.php?content= HTTP/1.1", upstream: 
http://192.168.xxxxx:80/index.php?content=", host: "www.xxxx", referrer: 
https://www.xxxxde/index.php?content="


this are my proxy settings


     proxy_buffering   on;
     proxy_buffer_size    32k;
     proxy_buffers        64   32k;
     client_body_buffer_size 256k;
     proxy_busy_buffers_size 128k;



thanks