Strict Standards: Only variables should be passed by ref - I need help please

Please I need help with this code. I have a reservation web page and is popping out that error:

<?php
    $result = mysql_query("SELECT * FROM internet_shop");
    while($row=mysql_fetch_assoc($result))
    {  
        // Loops 3 times if there are 3 returned rows... etc
        $a = $row['id'];
        $query = mysql_query("SELECT sum(qty) FROM rooinventory 
            where arrival <= '$arrival' 
            and departure >= '$departure' 
            and room='$a'");
        while($rows = mysql_fetch_array($query))
        {
            $inogbuwin = $rows['sum(qty)'];
        }
        $angavil = 1 - $inogbuwin;
        if($angavil > 0) {
            echo '<div class="product">
                <img src="img/products/'.$row['img'].'"                                  
                alt="'.htmlspecialchars($row['name']).'" 
                width="128" height="128" class="pngfix" />
                </div>';
        }
    }
?>

So far I've read the array for the values is wrong. Please just a light and I'll keep going on this....thanks in advance.