Nginx index.php forbidden sub-directory only!

[Mr. Hien]

Solved by remove " open_file_cache max=5000 inactive=20s;" from main
config file.
But someone can explain what problem caused.
Maybe bug?
Access URL http://example.com/wp-admin/index.php  works fine
While http://example.com/wp-admin/ give 403

Permission for wp-admin/index.php is 400, when I try chmod to 444,
problem solved. I running nginx in OpenVZ.