Fatal error: Call to a member function help

[Acers]

was trying to get some page into the who's online system. was doing pattern recognition. the code is like :

PHP Code:

elseif (preg_match("/topic\/(\d*)-\d*/", $userinfo['location'], $tester1))
                        {

                                $titlethrd = $DB_site->query("
                                SELECT title
                                FROM " . TABLE_PREFIX . "thread
                                WHERE threadid = " . intval($tester1[1]) . "
                                ");

                               
                                $userinfo['where'] = "<a href=\"search/topic/$tempo-1.html\"\">$titlethrd[title]</a>";


                        } 


idea being that if there is a match then in $tester1[1] i will have the thread id(which i do have , i have checked via echo. Now on the line

PHP Code:

$titlethrd = $DB_site->query(" 


i am getting
Fatal error: Call to a member function on a non-object

what does that mean?