Cannot access property WP::$public query_vars

Hello,

I have several mistakes in my error.log:
host: “www.enduro.de”
07/31/2015 16:17:15 [error] 26864 # 0: * 3540539 FastCGI sent to stderr: “PHP message: PHP Fatal error: Can not access property WP :: $ public_query_vars in / var / www / clients / client1 / web2 / web / wp-includes / class-wp.php on line 94 “while reading response headers from upstream, client: 144.76.14.84, server: enduro.de, request:” GET /index.php/feed/ HTTP / 1.1 “upstream” FastCGI: // UNIX: /var/lib/php5-fpm/web2.sock “

In the class-wp.php amenities in this section:
* Add name to list of public query variable.
*
*since 2.1.0
*
*param String $ qv query variable name.
* /
public function add_query_var ($ qv) {
if (! in_array ($ qv, $ this-> public_query_vars))
$ this-> public_query_vars [] = $ qv;
}

/ **

The line 94:
if (! in_array ($ qv, $ this-> public_query_vars))

Can help me, someone? Many Thanks!