PHP Download script - hanging at 99%

[facelessface]

I'm using a PHP script to force the download of files (i.e. to stop them opening in a web browser). However with any file larger than about 100k - the file stops at 99% for about 10-20 seconds, before it completes.

Any idea why this could happen? Code below...

$saveasname = basename($filename); 
Header('Content-Length: '.filesize($filename));
 Header('Content-Type: application/octetstream');
Header('Content-Type: application/force-download');
header("Content-Transfer-Encoding: binary");
header("Content-Disposition: attachment; filename=\"".$saveasname."\"");
// Output file 
readfile($filename);