Maybe the following might help you finding out the error:

BEGIN {
  print "Content-type: text/html\n\n";
}
[download]

This tries to send a content-type as early as possible. In combination with use CGI::Carp qw(fatalsToBrowser); you might find out better information about the problem.

Best regards,
perl -e "s>>*F>e=>y)\*martinF)stronat)=>print,print v8.8.8.32.11.32"