Nginx Helper filesize(): stat failed

I'm using nginx helper with WP Supercache and Wordpress Multisite in subdirectories (using the Map functionality to speed up access). However I'm getting this warning in my nginx log files.

2013/09/24 07:26:41 [error] 29476#0: *29306 FastCGI sent in stderr: "PHP message: PHP Warning: filesize(): stat failed for /var/www/mysite/wp-content/blogs.dir/4416/files/nginx-helper/nginx.log in /var/www/mysite/wp-content/plugins/nginx-helper/purger.php on line 288" while reading response header from upstream, client:, server: mysite, request: "POST /norm60132/wp-cron.php?doing_wp_cron=1379978796.7586300373077392578125 HTTP/1.0", upstream: "fastcgi://unix:/var/run/php5-fpm.sock:", host: "mysite"

Can you paste output for:

ls -l /var/www/mysite/wp-content/blogs.dir/4416/files/nginx-helper/nginx.log

Please check if that file is present there and has proper permission.