nginx错误日志出现大量open() failed (2: No such file or directory)

nginx的错误日志（error.log）里面出现大量如下的错误

2013/06/24 00:08:21 [error] 30159#0: *42212760 open() "/home/webadm/skin/frontend/base/default/images/brand_list/lbs_view.gif" failed (2: No such file or directory), client: 1xx.1xx.2xx.1xx, server: skin.xxx.com, request: "GET /frontend/base/default/images/brand_list/lbs_view.gif HTTP/1.0", host: "skin.xxx.com", referrer: "http://m.xxx.com/chaussures/baskets-femme/598-317080-3-p-baskets-montantes-cloutees-lbs818-lbs-noir.html"

由于在线服务器，配置文件比较庞大，无法贴出来，请教解决思路

补充：

此服务器是nginx做反向代理，后端还有3台nginx服务器接收www.xxx.com的请求，后端服务器不会出现这个问题

此服务器还做备用图片服务器，即skin.xxx.com，另外有一台主要的图片服务器skin.yyy.com也是用nginx搭建，里面有个主要的规则是：如果主图片服务器请求的文件不存在，则代理到备用图片服务器skin.xxx.com

if ( !-f $request_filename ){
        proxy_pass http://skin.xxx.com;
 }

而且，主图片服务器的错误日志也有大量的如下错误：

2013/06/23 00:07:16 [crit] 5739#0: *64206972 rename() "/home/webadm/skin/0000556071" to "/home/webadm/skin/" failed (20: Not a directory) while reading upstream, client: 120.196.212.213, server: skin.yyy.com, request: "GET / HTTP/1.1", upstream: "http://1xx.1xx.1y.1yy:80/", host: "skin.yyy.com"