Nginx – PHP FPM gives permission denied

I read several entries on why PHP-FPM might give me permission denied but I can not solve it.

The error logs read like:

    2013/04/20 23:33:28 [crit] 15479#0: *6 open() "/var/lib/nginx/tmp/fastcgi
/2/00/0000000002" failed (13: Permission denied) while reading upstream, client: 
99.999.999.999, server: example.net, request: "GET /wp-admin/ HTTP/1.1", 
upstream: "fastcgi://unix:/tmp/php-fpm.sock:", host: "example.net", referrer:    
"http://example.net/"

Im a little but lost:

1. I have set the /var/lib/nginx/tmp to ec2-user (i even +777 everything to check)
2. I have set the /tmp/php-fpm.sock to ec2-user
3. the nginx conf file is set to ec2-user
4. the php-conf is set to user and group ec2-user
5. ps aux gives ec2-user on all php-fpm and nginx processes

My Nginx Configuration includes a lot of files , the basic conf is:

user              ec2-user ec2-user;
worker_processes  5;  
error_log /opt/nginx/error.log;    
pid        /var/run/nginx.pid;    
events {
    worker_connections  1024;
}
http {
    include       mime.types;
    default_type  application/octet-stream;    
    log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
                      '$status $body_bytes_sent "$http_referer" '
                      '"$http_user_agent" "$http_x_forwarded_for"';
    access_log /opt/nginx/access.log main;    
    sendfile        on;
    keepalive_timeout  65;
    client_max_body_size 13m;
    index index.php index.html index.htm;
    upstream php {
       server unix:/tmp/php-fpm.sock;
    }
    include /etc/nginx/conf.d/*.conf;
    include /mnt/web/nginx/conf.d/*.conf;
}

my /etc/nginx/conf.d/ is empty
my /mnt/web/nginx/conf.d contain A LOT of website configurations which all include "wordpress.conf":

location / {
    try_files $uri $uri/ /index.php?$args;
}
rewrite /wp-admin$ $scheme://$host$uri/ permanent;
location ~* \.(js|css|png|jpg|jpeg|gif|ico)$ {
    expires 24h;
    log_not_found off;
}
location ~ \.php$ {
    try_files $uri =404;    
    fastcgi_split_path_info ^(.+\.php)(/.+)$;
    include fastcgi_params;
    fastcgi_index index.php;
    fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
    fastcgi_pass php;
}

My /opt/php/etc/php-fpm.conf:

include=/opt/php/etc/fpm.d/*.conf
pid = run/php-fpm.pid
error_log = log/php-fpm.log
log_level = notice
[www]
listen = /tmp/php-fpm.sock
user = ec2-user
group = ec2-user
pm = dynamic
pm.max_children = 250
pm.start_servers = 20
pm.min_spare_servers = 5
pm.max_spare_servers = 35
pm.max_requests = 500
pm.status_path = /fpm-status
ping.path = /fpm-ping
slowlog = log/$pool.log.slow
catch_workers_output = yes

UPDATE: found the problem, put it in the answer