Upstream prematurely closed connection while reading response header from upstream

I always got this error on my error.log

2008/12/12 09:20:06 [error] 7624#0: *5598 upstream prematurely closed
connection while reading response header from upstream, client:
125.160.44.41, server: domain.com, request: “GET
/www/delivery/lg.php?bannerid=104&campaignid=36&zoneid=33&channel_ids=,&loc=
http%3A%2F%2Ftv.kompas.com%2Fcontent%2Fview%2F4861%2F61&cb=978b16448a
HTTP/1.1”, upstream: “fastcgi://127.0.0.1:9000”, host: “domain.com”,
referrer: http://domain.com/www/delivery/afr.php?n=a4fc9429
<http://domain.com/www/delivery/afr.php?n=a4fc9429&zoneid=33&cb=INSERT_RANDO
M_NUMBER_HERE> &zoneid=33&cb=INSERT_RANDOM_NUMBER_HERE

It’s sometimes appear on my error log. I’m using nginx with php-fpm
patch

May someone explain why this happend? And how to fix it?