i don't know if this is enough you to help me but looking at this could you tell me what i could do to fix it?
$user_check = mysql_query("SELECT userdb_user_name FROM default_userdb WHERE userdb_user_name='$reciever'");
$user_check = mysql_num_rows($user_check);
Warning: mysql_num_rows(): supplied argument is not a valid MySQL result resource in /xx/xx/x/xx/xx/xx/xxxx/xxxxx/htdocs/xxxx/xxx/xxx.php