Reworked it a few minutes ago using the exact same syntax you showed and it still works for me so I am guessing that you did not have any size attributes assigned to the div and it was empty so it did not show.
Code:
<html>
<head>
<title></title>
</head>
<body>
<div style="width:500px;height:500px;background-image: url(images20/##Namevar##.jpg), url(images20/default.jpg);"><div>
</body>
</html>