请问一个Nginx的问题，页面经常出现502 Bad Gateway

系统是Ubuntu server 10.10 web 是nginx+uwsgi
页面经常出现502 Bad Gateway

查看连接状态：
ubuntu@D6.com:/var/log/nginx$ netstat -n | awk '/^tcp/ {++S[$NF]} END {for(a in S) print a, S[a]}'
FIN_WAIT2 28
SYN_RECV 21
TIME_WAIT 4726
ESTABLISHED 730
LAST_ACK 71
FIN_WAIT1 23

Log里面一直是这个错误：
2011/08/08 13:36:06 [error] 910#0: *42963834 upstream prematurely closed connection while reading response header from upstream, client: 127.0.0.1, server: 127.0.0.1, request: "GET /xxxc.om HTTP/1.0", upstream: "uwsgi://192.168.1.11:80", host: "test"
2011/08/08 13:36:06 [error] 910#0: *42963842 upstream prematurely closed connection while reading response header from upstream, client: 127.0.0.1, server: 127.0.0.1, request: "GET /xxxx.com HTTP/1.0", upstream: "uwsgi://192.168.1.10:80", host: "test"