Bad file descriptor with file download script

#!/usr/bin/perl -T
use strict; 
use warnings; 
use CGI; 
# Uncomment the next line only for debugging the script. 
use CGI::Carp qw/fatalsToBrowser/;
# the path to where the downloadable files are. 
# prefereably this should be above the web root folder. 
my $path_to_files = '/apps/actweb/cgi-bin';
my $q = CGI->new;
my $file = $q->param('file') or error('Error: No file selected.');
# here we untaint the filename and make sure there are no characters like / 
# in the name that could be used to download files from any folder on the website. 
# personally I don't even recommend you pass filenames to the script, but that 
# gets too complicated for a simple example of a download script. 
if ($file =~ /^(\w+[\w.-]+\.\w+)$/) { 
$file = $1; 
} 
else { 
error('Error: Unexpected characters in filename.'); 
}
if ($file) { 
download($file) or error('Error: an unknown error has occured. Try again.'); 
}
sub download {
# Uncomment the next line only for debugging the script 
#open(DLFILE, '<', "$path_to_files/$file") or die "Can't open file '$path_to_files/$file' : $!";
# Comment the next line if you uncomment the above line 
open(DLFILE, '<', "$path_to_files/$file") or return(0);
# this prints the download headers with the file size included 
# so you get a progress bar in the dialog box that displays during file downlaods. 
print $q->header(-type => 'application/x-download', 
-attachment => $file, 
'Content-length' => -s "$path_to_files/$file", 
);
binmode DLFILE; 
print while <DLFILE>; 
close (DLFILE); 
return(1); 
}
# This is a very generic error page. You should make a better one. 
sub error { 
print $q->header(), 
$q->start_html(-title=>'Error'), 
$q->h1($_), 
$q->end_html; 
exit(0); 
}