Problém setInterval

<?php
require_once "../ajax/refresh.php";
echo '<div id="sklo">';
  $result = $join_db->query("SELECT * FROM ".$_GET['rid']."_text WHERE pro='all' ORDER BY id DESC LIMIT 0, 20");
   while($s_r = $result->fetch_row()){
 
 // if (($text["od"] == $nick) AND ($text["pro"] != "all")){
 // $znak = "->".$text["pro"].": ";
 // }
 // if ($text["pro"] == $nick){
 // $znak = "->$nick: ";
 // }
 if ($s_r["pro"] == "all"){
 $znak = ":";
 }


 if (($s_r["od"] != "System") AND ($s_r["od"] != "".$_SESSION['user_nick']."") AND ($s_r["od"] != "")){
$nahr_co = array($_SESSION['user_nick']);
$nahr_cim = array("<b>".$_SESSION['user_nick']."</b>");

$btext = str_replace($nahr_co, $nahr_cim, $s_r[4]);
}
else{
$btext = $s_r[4];
}



// převod odkazů
if ((!eregi("<a href", $btext)) AND (!eregi("<img", $btext))){

 $btext = eregi_replace('http://([a-zA-Z0-9\?=%&/\$\._äëöü#;-]*)', '<a href="http://\\1" target="_blank">http://\\1</a>', $btext);
 }

$od_nick = $s_r[2];

$od_nick = preg_replace('/\*(\d+)\*/', '', $od_nick);

echo "
<p>".$s_r[1]."<b> ".$od_nick."$znak </b> ".$btext."</p></font>
"; 
}
echo '</div>'; 
?>

try {
    $join_db = new mysqli('localhost', 'root', 'vertrigo', 'pokus');
    if(!$join_db){
        throw new Exception('connect databases faild!');
    }
}
catch (Exception $e){
    echo  $e->getMessage();
}
// check mysqli_connect_errno
try {
    $join_db = new mysqli('localhost', 'root', 'vertrigo', 'oikus');
    if(mysqli_connect_errno()){
        throw new Exception('connect databases faild!');
    }
}
catch (Exception $e){
    echo  $e->getMessage();
}

<script type="text/javascript">

function ajaxFunction()
{
var xmlHttp;
try {
xmlHttp=new XMLHttpRequest();
}

catch (e) {
try {
xmlHttp=new ActiveXObject("Msxml2.XMLHTTP");
}
catch (e) {
try {
xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");
}
catch (e) {
alert("Váš prohlížeč nepodporuje AJAX");
return false;
}
}
}
xmlHttp.onreadystatechange=function() {
if(xmlHttp.readyState==4) {
var x=document.getElementById("sklo");
x.innerHTML = xmlHttp.responseText;
}
}
xmlHttp.open("GET","print_text.php",true);
xmlHttp.send(null);

}
//var interval = 5;
//setTimeout('ajaxFunction()', interval*1000);

window.setInterval('ajaxFunction()', 5000); 
</script>

<a href="window.php?rid=<? echo $_GET['rid'];?>" onclick="ajaxFunction()">Obnovit</a>

Fatal error: Call to a member function query() on a non-object in C:\Software\VertrigoServ\www\pokus\print_text.php on line 4