MYSQL Fehler!

[Simon]

Hallo,
ich verzweifel gerade, finde den Fehler nicht:

Fehlermeldung: Unknown column 'adf' in 'where clause'
Warning: mysql_num_rows(): supplied argument is not a valid MySQL result resource in

Code:   if(isset($username) && ($userpass)) {
    $username = trim($username);
    $userpass = trim($userpass);
   $user_erg = mysql_query("SELECT user.id AS USER_ID, user.username AS USER_USERNAME, user.userpass, user.usertask, usertask.id, usertask.description AS USERTASK_DESCRIPTION FROM cms_user AS user LEFT JOIN cms_usertask AS usertask ON user.usertask = usertask.id WHERE user.status = 1 AND user.username = ".$username." AND user.userpass = ".$userpass."");
   echo mysql_error();
      if(mysql_num_rows($user_erg)>0) {
      $user_row = mysql_fetch_array($user_erg);
        $_SESSION[USER_ID] = $user_row['USER_ID'];
     $_SESSION[USERNAME] = $user_row['USERNAME'];
     $_SESSION[USERTASK] = $user_row['USERTASK_DESCRIPTION'];
     echo 'OK.';
   } else {
     $user_error[] = $GLOBALS['user_false_userpass'];
   }
  }

Gruß .. Simon