Warning: Cannot modify header information - headers already sent

Jeg får følgende fejl på min side :

Warning: Cannot modify header information - headers already sent by (output started at /home/web/web492/connect.php:20) in /home/web/web492/index.php on line 35

Toppen af min PHP side der melder fejl ser sådan her ud :

<?
session_start();
header("Pragma: no-cache");
header("Cache-Control: no-cache");
header("Cache-Control: no-store");
setcookie("eventid2"," ",time()-3600);
setcookie("nyhedsid2"," ",time()-3600);

require("connect.php");

if(!$uniktaeller){

$ugenr = date("W");


$uge = mysql_query ("SELECT taeller FROM uge_statistik WHERE uge = '$ugenr'");
if (mysql_num_rows($uge) > 0)
                {
while ($ugedata = mysql_fetch_array($uge))
                    {

$ugetaeller = $ugedata["taeller"]+1;
         
          $ins = mysql_query("UPDATE uge_statistik SET taeller = '$ugetaeller' WHERE uge ='$ugenr'");
}

}
else{

mysql_query("INSERT INTO uge_statistik (uge, taeller) VALUES ('$ugenr', '1')");
}

setcookie(uniktaeller, "1", time()+60*60*24);
}

if($eventid){

setcookie(eventid2, $eventid, time()+120);
}
if($nyhedsid){

setcookie(nyhedsid2, $nyhedsid, time()+120);
}

?>

Linie 35 er denne linie :
setcookie(uniktaeller, "1", time()+60*60*24);

Hvad er fejlen???

I connect.php er der kun et MySql login..