After careful examination and testing, you weren't returning full http headers, which you tried to fix up with capture, but all you need is nph:

D:\>perl -MCGI -le"print CGI->header"
Content-Type: text/html



D:\>perl -MCGI -le"print CGI->header(-nph => 1)"
HTTP/1.0 200 OK
Server: cmdline
Date: Fri, 20 Feb 2009 10:35:31 GMT
Content-Type: text/html



D:\>
[download]

USING NPH SCRIPTS, No-Parse Headers