Did you change to this?
PHP Code:
<script language="JavaScript">
<!-- START HIDE
function whodownloaded(attachmentid) {
window.open
("whodownloaded.php?s=$session[sessionhash]&attachmentid=" + attachmentid,
"whodownloaded", "toolbar=no,scrollbars=yes,resizable=no,width=240,height=300, top=50, left=50"); }
-->
</script>
The function line needs to start on it's own line.