Signup from non-VB page

[Liquid1ce]

hmmm i made a page but the data i want posted on a forum say id 20
I tried using this code to submit that data

                        $DB_site->query("
                                INSERT INTO " . TABLE_PREFIX . "thread(threadid, title, lastpost, forumid, open, replycount, postusername, postuserid, lastposter, dateline,iconid, visible, attach, similar)
                                VALUES (NULL,'".addslashes(htmlspecialchars($subject))."','".time()."','$forumid','1','0','".addslashes($postusername)."','$bbuserinfo[userid]','".addslashes($postusername)."','".time()."','$iconid','$visible','0')");

But i just get a error sayin

Fatal error: Call to a member function on a non-object in /var/www/signup.php on line 172

line 172 =

                         $DB_site->query("

on the above code
Any help>?