With the code shown, not sure what's wrong. I've just taken your example and, with a few tweaks, the following runs fine on my box:

<FORM ACTION="path_to_form.cgi" METHOD="POST" ENCTYPE="multipart/form-
+data">
<INPUT TYPE="text" NAME="filename" SIZE="10" MAXLENGTH="50">
<INPUT TYPE="FILE" NAME="upfile">
<INPUT TYPE="submit" VALUE="upload">
</FORM>



#!/usr/bin/perl -w

use strict;
use warnings;
use CGI qw(:standard);
use CGI::Carp 'fatalsToBrowser';

$CGI::DISABLE_UPLOADS = 0;
$CGI::POST_MAX = 52428800;

my $SAVE_DIRECTORY = "/tmp";
my $query=new CGI;

my $filename = $query->param("filename") or die "no filename";

# you need to check that the filename only contains sane characters
# otherwise you could have users writing anywhere in the file system
die "bad filename" unless $filename =~ m/^\w+$/;

my $fh       = $query->upload("upfile") or die "no file";

# you realise this could allow multiple users to write to the same
# filename at the same time. probably not what you want.
open(OUTFILE, ">$SAVE_DIRECTORY\/$filename") or die "open failed ($!)"
+;
binmode OUTFILE;
my ($bytes, $buffer, $size);
while ($bytes = read($fh,$buffer,1024)) {
    $size+=$bytes;
    print OUTFILE $buffer;
};
# read can fail with undef - you need to check :-)
die "read failure ($!)" unless defined($bytes);
close(OUTFILE);

print $query->header;
print "$filename uploaded: $size bytes" if $size > 0;
[download]

Try the above on your machine and see if it works

Personally, I would suspect your HTML - it looks like you're not passing upfile for some reason...

The best way of solving this sort of problem is to actually write a smaller version of the code that demonstrates the problem. Once you have your "other code" and "other html" out of the way the error will probably become obvious :-)