รบกวน ขอคำแนะนำคะ Warning: in_array() [function.in-array]: Wrong datatype for second argument

include_once("connect_page.php");
$sql2="select id_prd, name_prd  from tb_product";
	mysql_query("SET character_set_client=utf8");
	$result2=mysql_db_query($dbname,$sql2);
	while ($rs2=mysql_fetch_array($result2))
	{
		$id_prd=$rs2[id_prd];
		$name_prd=$rs2[name_prd];
					
		echo "<h3>".$name_prd."</h3><hr color='#ff0066'>";
echo "<a href='basket_added.php?id_prd=$id_prd'>เลือกซื้อ &nbsp;</a>";
	}

<?php
session_start();
session_register("sess_id");
session_register("sess_name");
session_register("sess_price");
session_register("sess_num");
if(count($sess_id)=="0"){
	$check=1;
}else if(!in_array($id_prd,$sess_id)){ // ERROR line 9
	$check=1;
	}
if($check==1){
	include_once("connect.php");
	$sql="select * from tb_product where id_prd=$id_prd";
	$result=mysql_db_query($dbname,$sql);
	$rs=mysql_fetch_array($result);
	[$sess_id[]=$rs[id_prd];   // ERROR line 17
	$sess_name[]=$rs[name_prd];
	$sess_price[]=$rs[price_prd];
	$sess_num[]=1;
}
//header("location:basket.php");
echo "OK -> ".$sess_id." : ".$sess_name;
?>