Sorry,

/usr/local/nginx/sbin/nginx -V
nginx: nginx version: nginx/1.0.4
nginx: built by gcc 4.4.3 (Ubuntu 4.4.3-4ubuntu5)
nginx: TLS SNI support enabled
nginx: configure arguments: --with-http_ssl_module --with-debug --with-http_gzip_static_module --with-http_stub_status_module

Part of Config:

http {
proxy_cache_path /usr/local/nginx/html/cache levels=1:2 keys_zone=my-cache:8m max_size=1000m inactive=600m;
proxy_temp_path /usr/local/nginx/html/cache/tmp;
}

server {

upstream backend-img {
server x.x.x.x;
server x.x.x.x;
}


location ~* \.(png|gif|jpg|bmp|jpeg|swf|fla|js|css)$ {
proxy_buffering on;
proxy_cache my-cache;
proxy_cache_valid 200 302 120m;
#proxy_cache_valid 404 1m;
expires 86400;
proxy_pass http://backend-img;
}
}

Debug log:

2011/06/14 23:41:22 [debug] 4704#0: *27136 http copy filter: "/201103/04/I_M_44112691.JPG?"
2011/06/14 23:41:22 [debug] 4717#0: *27130 finalize http upstream request: -1
2011/06/14 23:41:22 [debug] 4704#0: *27136 http postpone filter "/201103/04/I_M_44112691.JPG?" 00007FFF0E740E10
2011/06/14 23:41:22 [debug] 4717#0: *27130 finalize http proxy request
2011/06/14 23:41:22 [debug] 4704#0: *27136 write new buf t:0 f:0 0000000000000000, pos 0000000000000000, size: 0 file: 0, size: 0
2011/06/14 23:41:22 [debug] 4717#0: *27130 free rr peer 2 0
2011/06/14 23:41:22 [debug] 4704#0: *27136 http write filter: l:1 f:0 s:0
2011/06/14 23:41:22 [debug] 4717#0: *27130 close http upstream connection: 54
2011/06/14 23:41:22 [debug] 4704#0: *27136 http copy filter: 0 "/201103/04/I_M_44112691.JPG?"
2011/06/14 23:41:22 [debug] 4717#0: *27130 event timer del: 54: 1308106282252
2011/06/14 23:41:22 [debug] 4704#0: *27136 http finalize request: 0, "/201103/04/I_M_44112691.JPG?" a:1, c:1
2011/06/14 23:41:22 [debug] 4717#0: *27130 reusable connection: 0
2011/06/14 23:41:22 [debug] 4704#0: *27136 http request count:1 blk:0
2011/06/14 23:41:22 [debug] 4704#0: *27136 http close request
2011/06/14 23:41:22 [debug] 4704#0: *27136 http log handler
2011/06/14 23:41:22 [debug] 4704#0: *27136 posix_memalign: 00000000023BCBD0:4096 @16
2011/06/14 23:41:22 [debug] 4704#0: *27136 run cleanup: 0000000002396688
2011/06/14 23:41:22 [debug] 4704#0: *27136 free: 000000000239CBC0
2011/06/14 23:41:22 [debug] 4704#0: *27136 free: 0000000002395740, unused: 2
2011/06/14 23:41:22 [debug] 4704#0: *27136 free: 0000000002398760, unused: 80
2011/06/14 23:41:22 [debug] 4704#0: *27136 free: 00000000023BCBD0, unused: 3560
2011/06/14 23:41:22 [debug] 4717#0: *27130 http finalize request: -1, "/201010/01/I_P_41105460.JPG?" a:1, c:1
2011/06/14 23:41:22 [debug] 4704#0: *27136 close http connection: 102
2011/06/14 23:41:22 [debug] 4717#0: *27130 http terminate request count:1
2011/06/14 23:41:22 [debug] 4704#0: *27136 reusable connection: 0
2011/06/14 23:41:22 [debug] 4717#0: *27130 http terminate cleanup count:1 blk:0
2011/06/14 23:41:22 [debug] 4717#0: *27130 http posted request: "/201010/01/I_P_41105460.JPG?"
2011/06/14 23:41:22 [debug] 4717#0: *27130 http terminate handler count:1
2011/06/14 23:41:22 [debug] 4717#0: *27130 http request count:1 blk:0
2011/06/14 23:41:22 [debug] 4704#0: *27136 free: 0000000002396750
2011/06/14 23:41:22 [debug] 4717#0: *27130 http close request
2011/06/14 23:41:22 [debug] 4704#0: *27136 free: 0000000002391D00
2011/06/14 23:41:22 [debug] 4717#0: *27130 http log handler
2011/06/14 23:41:22 [debug] 4704#0: *27136 free: 0000000002391700
2011/06/14 23:41:22 [debug] 4704#0: *27136 free: 0000000002393230, unused: 8
2011/06/14 23:41:22 [debug] 4704#0: *27136 free: 0000000002391BF0, unused: 0
2011/06/14 23:41:22 [debug] 4717#0: *27130 run cleanup: 000000000238E7E0
2011/06/14 23:41:22 [debug] 4704#0: posted event 0000000000000000
2011/06/14 23:41:22 [debug] 4717#0: *27130 file cleanup: fd:53
2011/06/14 23:41:22 [debug] 4704#0: worker cycle
2011/06/14 23:41:22 [debug] 4704#0: accept mutex locked
2011/06/14 23:41:22 [debug] 4717#0: *27130 run cleanup: 000000000238E780
2011/06/14 23:41:22 [debug] 4704#0: epoll timer: 7044
2011/06/14 23:41:22 [debug] 4717#0: *27130 http file cache cleanup
2011/06/14 23:41:22 [alert] 4717#0: *27130 stalled cache updating, error:0 while closing request, client: 189.58.56.239, server: 0.0.0.0:80
2011/06/14 23:41:22 [debug] 4717#0: *27130 http file cache free, fd: 53
2011/06/14 23:41:22 [debug] 4717#0: shmtx lock
2011/06/14 23:41:22 [debug] 4717#0: shmtx unlock
2011/06/14 23:41:22 [debug] 4717#0: *27130 free: 00000000023A9CB0
2011/06/14 23:41:22 [debug] 4717#0: *27130 free: 000000000238D830, unused: 0
2011/06/14 23:41:22 [debug] 4717#0: *27130 free: 00000000023654E0, unused: 86
2011/06/14 23:41:22 [debug] 4717#0: *27130 close http connection: 47
2011/06/14 23:41:22 [debug] 4717#0: *27130 reusable connection: 0
2011/06/14 23:41:22 [debug] 4717#0: *27130 free: 00000000023950F0
2011/06/14 23:41:22 [debug] 4717#0: *27130 free: 0000000002370520
2011/06/14 23:41:22 [debug] 4717#0: *27130 free: 000000000235E100, unused: 8
2011/06/14 23:41:22 [debug] 4717#0: *27130 free: 00000000023A9980, unused: 128
2011/06/14 23:41:22 [debug] 4717#0: timer delta: 2
2011/06/14 23:41:22 [debug] 4717#0: posted events 0000000000000000
2011/06/14 23:41:22 [debug] 4717#0: worker cycle
2011/06/14 23:41:22 [debug] 4717#0: accept mutex lock failed: 0
2011/06/14 23:41:22 [debug] 4717#0: epoll timer: 500
2011/06/14 23:41:22 [debug] 4722#0: epoll: fd:65 ev:0005 d:00007F6C76ED9390
2011/06/14 23:41:22 [debug] 4722#0: *26419 http upstream request: "/imovel/flat-alugar/sp/sao-paulo/jardins/90665944.iw?precomaximo=2000&quartos=1,2,3,4,5&idtipoimovel=2,1,4&idlocalidade=118,34,121,478,127,49,53,129,130,464,139&idlocalizacao=1&idsublocalizacao=3"
2011/06/14 23:41:22 [debug] 4722#0: *26419 http upstream process header
2011/06/14 23:41:22 [debug] 4722#0: *26419 malloc: 00000000023986B0:131072
2011/06/14 23:41:22 [debug] 4722#0: *26419 posix_memalign: 0000000002389DA0:4096 @16
2011/06/14 23:41:22 [debug] 4722#0: *26419 recv: fd:65 2896 of 131072
2011/06/14 23:41:22 [debug] 4722#0: *26419 http proxy status 200 "200 OK"
2011/06/14 23:41:22 [debug] 4722#0: *26419 http proxy header: "Cache-Control: private"
2011/06/14 23:41:22 [debug] 4722#0: *26419 http proxy header: "Content-Type: text/html; charset=utf-8"
2011/06/14 23:41:22 [debug] 4722#0: *26419 http proxy header: "Content-Encoding: gzip"
2011/06/14 23:41:22 [debug] 4722#0: *26419 http proxy header: "Server: Microsoft-IIS/7.5"
2011/06/14 23:41:22 [debug] 4722#0: *26419 http proxy header: "X-AspNet-Version: 2.0.50727"
2011/06/14 23:41:22 [debug] 4722#0: *26419 http proxy header: "X-Powered-By: ASP.NET"
2011/06/14 23:41:22 [debug] 4722#0: *26419 http proxy header: "Date: Wed, 15 Jun 2011 02:43:53 GMT"
2011/06/14 23:41:22 [debug] 4722#0: *26419 http proxy header: "Connection: close"
2011/06/14 23:41:22 [debug] 4722#0: *26419 http proxy header: "Content-Length: 52416"
2011/06/14 23:41:22 [debug] 4722#0: *26419 http proxy header done
2011/06/14 23:41:22 [debug] 4722#0: *26419 HTTP/1.1 200 OK^M
Server: nginx/1.0.4^M
Date: Wed, 15 Jun 2011 02:41:22 GMT^M
Content-Type: text/html; charset=utf-8^M
Connection: keep-alive^M
Cache-Control: private^M
Content-Encoding: gzip^M
Content-Length: 52416^M


Thanks.