As I said, the file that is coming from the download is either a problem or does not work specifically on my server.
This error was occurring when I searched with a custom field:
[Wed Jul 05 20:07:03 2017] [error] [client 177.143.236.173] PHP Warning:  urldecode() expects parameter 1 to be string, array given in /home/folder/oscalss.domain.com/oc-includes/osclass/classes/Rewrite.php on line 192, referer: http://oscalss.domain.com/index.php?page=search&sOrder=dt_pub_date&iOrderType=desc&sCategory=96
The problem is in the: /oc-includes/osclass/classes/Rewrite.php from version 3.7.3
When i change the code from version 3.7.3:
public function extractParams($uri = '')
        {
            $uri_array = explode('?', $uri);
            $length_i = count($uri_array);
            for($var_i = 1;$var_i<$length_i;$var_i++) {
                parse_str($uri_array[$var_i], $parsedVars);
                foreach($parsedVars as $k => $v) {
                    Params::setParam($k, urldecode($v));
                }
            }
        }
To code from 3.6.1:
public function extractParams($uri = '')
        {
            $uri_array = explode('?', $uri);
            $length_i = count($uri_array);
            for($var_i = 1;$var_i<$length_i;$var_i++) {
                if(preg_match_all('|&([^=]+)=([^&]*)|', '&'.$uri_array[$var_i].'&', $matches)) {
                    $length = count($matches[1]);
                    for($var_k = 0;$var_k<$length;$var_k++) {
                        Params::setParam($matches[1][$var_k], $matches[2][$var_k]);
                    }
                }
            }
        }
Now everything works normally.