Warning: mysql_fetch_assoc(): supplied argument is not a valid

<? 
if($data->copheat > 99){
			$tijd  = rand(600,3600);
			mysql_query("UPDATE `users` 
						SET `gevangenis`='"  . $tijd . "',`copheat`='0',`baktijd`=NOW() 
						WHERE `login`='" . $data->login .  "'");
	}
	
	   	$dbres = mysql_query("SELECT *,UNIX_TIMESTAMP(`tijd`) AS `baktijd`,0 FROM `users` WHERE `login`='" . $data->login . "'");
    	$fetch = mysql_fetch_assoc($dbres);


		
    	$verschil = $fetch['baktijd'] - 3600 + $data->gevangenis - time();
    		if($fetch['baktijd'] + $data->gevangenis > time()){
    			header("Location: $sitelink/jail.php");
            
	
if($data->copheat > 99){
			$tijd  = rand(600,3600);
			mysql_query("UPDATE `users` SET `gevangenis`='"  . $tijd . "',`copheat`='0' WHERE `login`='" . $data->login .  "'");	
	
	
	   ?>