It's better to mark a post as updated. Again without seeing a repeatable example (see previous links) that demonstrates the problem it's difficult to help.

#!/usr/bin/perl
use strict;
use warnings;

my $derp = 'X' x 40000;
open (my $fh, '>', 'derp.txt') or die "can't open derp.txt: $!";
print $fh $derp;
close($fh);
[download]

ls -al derp.txt 
-rw------- 1 marto marto 40000 Sep 21 09:37 derp.txt
[download]

See also open, three arg open, migrating to modern perl.