Nginx Owncloud 4 produces “No input file specified.”

Question

I'm trying to setup an Owncloud 4 instance with nginx as a webserver. The host device is a Raspberry Pi with preinstalled Debian 6. When I try to open the URL to the Owncloud installation in a browser, I get a No input file specified. The installation is placed in /var/www/owncloud/owncloud. I use spawn_fcgi for cgi.
My nginx configurationfile /etc/nginx/sites-available/default looks like this:

server {

    listen   80; ## listen for ipv4
    #listen   [::]:80 default ipv6only=on; ## listen for ipv6

    server_name raspberrypi;

    access_log  /var/log/nginx/localhost.access.log;

    root /var/www/owncloud/owncloud/;
    index index.php;

    # deny direct access
    location ~ ^/(data|config|\.ht|db_structure\.xml|README) {
            deny all;
    }

    # default try order
    location / {
            try_files $uri $uri/  @webdav;
    }

    # owncloud WebDAV
    location @webdav {
            fastcgi_split_path_info ^(.+\.php)(/.*)$;
            fastcgi_pass 127.0.0.1:9000; # or use php-fpm with: "unix:/var/run/php-fpm/php-fpm.sock;"
            fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
            include fastcgi_params;
    }


    # enable php
    location ~ \.php$ {
            include fastcgi_params;
            fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
            fastcgi_pass 127.0.0.1:9000; # or use php-fpm with: "unix:/var/run/php-fpm/php-fpm.sock;"
    }

    location /doc {
            root   /usr/share;
            autoindex on;
            allow 127.0.0.1;
            deny all;
    }

    location /images {
            root   /usr/share;
            autoindex on;
    }

}

My /etc/nginx/nginx.conf looks like this:

user www-data;
worker_processes  1;

error_log  /var/log/nginx/error.log;  
pid        /var/run/nginx.pid;

events {
worker_connections  1024;
# multi_accept on;
}

http {
include       /etc/nginx/mime.types;

access_log  /var/log/nginx/access.log;

sendfile        on;
#tcp_nopush     on;

#keepalive_timeout  0;
keepalive_timeout  65;
tcp_nodelay        on;

gzip  on;
gzip_disable "MSIE [1-6]\.(?!.*SV1)";

include /etc/nginx/conf.d/*.conf;
include /etc/nginx/sites-enabled/*;
}

Can you help me to find the misconfiguration?