No PHP message is given in error.log

Hello,

every few seconds I get this error in my error.log:
FastCGI sent in stderr: "PHP message:" while reading response header from upstream, client: ..., server: www.test.de, request: "GET /forum HTTP/1.1", upstream: "fastcgi://unix:/var/run/php5-fpm.sock:", host: "www.test.de", referrer: "http://www.test.de/"

No message is given here and I don't know how to resolve this. Could my virtual host be here the problem?

Here the virtual host file:

server {
listen 80; ## listen for ipv4; this line is default and implied
listen [::]:80; ## listen for ipv6
server_name test.de
return 301 $scheme://www.test.de$request_uri;
}
server {
listen 80 default_server;
listen [::]:80 default_server ipv6only=on;

root /var/www/test;
index index.php index.html index.htm;

# Make site accessible from
server_name www.test.de;

access_log /var/log/nginx/test_access.log;
error_log /var/log/nginx/test_error.log;

location / {
# Search Engine Friendly URLs for Joomla CMS
try_files $uri $uri/ /index.php?$args;
proxy_read_timeout 1500;
}

# administrator page for CMS
location /administrator {
auth_basic "Restricted";
auth_basic_user_file /var/www/.htpasswd;
# fuer administrator/index.php
location ~ \.php$ {
fastcgi_split_path_info ^(.+\.php)(/.+)$;
fastcgi_pass unix:/var/run/php5-fpm.sock;
fastcgi_index index.php;
fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
include fastcgi_params;
}
}

error_page 404 /404.html;
error_page 500 502 503 504 /50x.html;
location = /50x.html {
root /usr/share/nginx/html;
}

location ~ \.php$ {
try_files $uri =404;
fastcgi_split_path_info ^(.+\.php)(/.+)$;
fastcgi_pass unix:/var/run/php5-fpm.sock;
fastcgi_index index.php;
fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
include fastcgi_params;
}

# cache control
location ~* \.(jpg|jpeg|png|gif|ico|css|js)$ {
expires 7d;
}

# deny running scripts inside writable directories
location ~* /(images|cache|media|logs|tmp)/.*\.(php|pl|py|jsp|asp|sh|cgi)$ {
return 403;
error_page 403 /403_error.html;
}

# location ~ /\. { deny all; }
}



I'm using ubuntu 14.04 with nginx 1.4.6

Regards