Drupal 6+；Imagecache+；nginx=无图像

我已经在nginx上安装了Drupal 6，但是我在imagecache上遇到了问题-查看任何图像都会生成空白屏幕

已安装PHP GD：

# php -m | grep gd
gd

777站点上文件夹及其所有内容：

ls -l | grep sites
drwxrwxrwx  4 nginx nginx      4096 Jan 12 23:36 sites

vhost.conf：

location / {
            # This is cool because no php is touched for static content
            try_files $uri @rewrite;
    }

    location @rewrite {
            # You have 2 options here
            # For D7 and above:
            # Clean URLs are handled in drupal_environment_initialize().
            #rewrite ^ /index.php;
            # For Drupal 6 and bwlow:
            # Some modules enforce no slash (/) at the end of the URL
            # Else this rewrite block wouldn't be needed (GlobalRedirect)
            rewrite ^/(.*)$ /index.php?q=$1;
    }

    # Fighting with Styles? This little gem is amazing.
    # This is for D6
    location ~ ^/sites/.*/files/imagecache/ {
    # This is for D7 and D8
    #location ~ ^/sites/.*/files/styles/ {
            try_files $uri @rewrite;
    }

Drupal日志中存在错误：

imagecache  2014-01-13 21:29    404: Unable to find low.jpg guest

nginx error.log（仅在access.log=404）或php错误日志中没有错误

文件存在于

/sites/default/files/

imagecache_sample.png在打开imagecache模块后正确创建

有什么想法吗