in include/class.osticket.php

change 

function get_path_info() {
    if(isset($_SERVER['PATH_INFO']))
        return $_SERVER['PATH_INFO'];

    if(isset($_SERVER['ORIG_PATH_INFO']))
        return $_SERVER['ORIG_PATH_INFO'];

    //TODO: conruct possible path info.

    return null;
}

to

static function get_path_info() {
    if(isset($_SERVER['PATH_INFO']) && !empty($_SERVER['PATH_INFO']))
        return $_SERVER['PATH_INFO'];

    if(isset($_SERVER['ORIG_PATH_INFO']) && !empty($_SERVER['ORIG_PATH_INFO']))
        return $_SERVER['ORIG_PATH_INFO'];

    $request_uri = preg_replace('@\?.*$@', '', $_SERVER['REQUEST_URI']);

    if (strpos($request_uri, $_SERVER['SCRIPT_NAME']) !== false) {
        $guessed_pathinfo = preg_replace('#^'.preg_quote($_SERVER['SCRIPT_NAME']).'#', '', $request_uri);
    } else {
        $guessed_pathinfo = preg_replace('#^'.preg_quote(preg_replace('@/([^/]+)$@', '', $_SERVER['SCRIPT_NAME'])).'#', '', $request_uri);
    }
    if (!empty($guessed_pathinfo))
        return $guessed_pathinfo;

    return null;
}