Debian – FastCGI Error Access to the script denied

I think your max_children is too low

<value name="max_children">3</value>

Also you can try switching from TCP port to unix socket for php-fpm:

php-fpm.conf

<value name="listen_address">/tmp/php.sock</value>

nginx.conf

fastcgi_pass unix:/tmp/php.sock;

Elaborated:

1. Unix sockets are ~20% faster
2. You don't use time-wait sockets for each connect

Two additional FastCGI parameters are required.

fastcgi_param SERVER_PORT "80";
fastcgi_param SCRIPT_NAME $fastcgi_script_name;

Credit goes to KnyghtMare from the #mono IRC channel for his test script. By elimination, the required parameters for the nginx conf were found. Usage note: you might have to change the IP and port number on the last line, and HTTP_HOST.

SERVER_SOFTWARE="lighttpd/1.4.26" \
SERVER_NAME="127.0.0.1" \
GATEWAY_INTERFACE="CGI/1.1" \
SERVER_PORT="80" \
SERVER_ADDR="127.0.0.1" \
REMOTE_PORT="28886" \
REMOTE_ADDR="127.0.0.1" \
SCRIPT_NAME="/" \
PATH_INFO="" \
SCRIPT_FILENAME="/var/www/" \
DOCUMENT_ROOT="/var/www/" \
REQUEST_URI="/" \
QUERY_STRING="" \
REQUEST_METHOD="GET" \
REDIRECT_STATUS="200" \
SERVER_PROTOCOL="HTTP/1.1" \
HTTP_HOST="arch" \
HTTP_CONNECTION="keep-alive" \
HTTP_CACHE_CONTROL="max-age=0" \
HTTP_USER_AGENT="Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/535.11 (KHTML, like Gecko) Chrome/17.0.963.83 Safari/535.11" \
HTTP_ACCEPT="text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8" \
HTTP_ACCEPT_ENCODING="gzip,deflate" \
HTTP_ACCEPT_LANGUAGE="en-US,en;q=0.8" \
HTTP_ACCEPT_CHARSET="ISO-8859-1,utf-8;q=0.7,*;q=0.3" \
cgi-fcgi -bind -connect 127.0.0.1:9000

After some more modifications to get resource files working, this is the current configuration:

server
{
        listen 80;
        server_name arch;

        access_log /var/www/test/log/access.log;
        error_log /var/www/test/log/error.log debug;

        root /var/www/test/public;

        location /
        {
                try_files $uri @proxy;
        }

        location @proxy
        {
                fastcgi_index /Home;
                fastcgi_pass 127.0.0.1:9000;
                fastcgi_param PATH_INFO "";
                fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
                fastcgi_param SERVER_PORT $server_port;
                fastcgi_param SCRIPT_NAME $fastcgi_script_name;
        }
}