welcome to WebmasterWorld [webmasterworld.com], siriusfire!

is the action atribute value of the form tag referring to the script url and do you have a method="post" attribute on that tag?
are you writing a Content-type header?
are there any clues in your server log files?

Thanks fro the welcome Phranque

Answers:

Yes,yes
I think so...
I can't see anything from the log files really indicating what is wrong!

This is the Form HTML:

 <form action="/cgi-bin/upload.cgi" method="post" 
enctype="multipart/form-data">
  <p>Photo to Upload: <input type="file" name="photo" /></p>
  <p>Your Email Address: <input type="text" name="email_address" /></p>
  <p><input type="submit" name="Submit" value="Submit Form" /></p>
 </form>

And this is the CGI script:

#!/usr/bin/perl

use strict;
use warnings;
use CGI;
use CGI::Carp qw/fatalsToBrowser/;
use File::Basename;

# set the maximum limit for file uploads
$CGI::POST_MAX = 1024 * 5000;

# change to 1 (one) to disable file uploads
$CGI::DISABLE_UPLOADS = 0; #1 disables uploads, 0 enables uploads

my $query = new CGI;

unless ($CGI::VERSION >= 2.47) {
 print $query->header(),
   $query->start_html(),
   'Your version of CGI.pm is too old. You must have verison 2.47 or higher to use this script.',
   $query->end_html;
 exit(0);
}

my $upload_dir = "/home/MYHOST/MYWEBSITE/user/htdocs/upload";

# a list of valid characters that can be in filenames
my $filename_characters = 'a-zA-Z0-9_.-';

my $file = $query->param("photo");
my $email_address = $query->param("email_address");

# get the filename and the file extension
# this could be used to filter out unwanted filetypes
# see the File::Basename documentation for details
my ($filename,undef,$ext) = fileparse($file,qr{\..*});

# convert spaces to underscores "_"
$filename =~ tr/ /_/;

# remove illegal characters
$filename =~ s/[^$filename_characters]//g;

# append extension to filename
$filename .= $ext;

# satisfy taint checking
if ($filename =~ /^([$filename_characters]+)$/) {
 $filename = $1;
}
else{
 print $query->header(),
   $query->start_html(),
   'The filename is not valid. Filenames can only contain these characters: $filename_characters',
   $query->end_html;
 exit(0);
}

my $upload_filehandle = $query->upload("photo");


open (UPLOADFILE, ">$upload_dir/$filename") or die "$!";
binmode UPLOADFILE;
while ( <$upload_filehandle> ) {
 print UPLOADFILE;
}
close UPLOADFILE;

print $query->header(),
  $query->start_html(-title=>'Upload Successful'),
  $query->p('Thanks for uploading your photo!'),
  $query->p("Your email address: $email_address"),
  $query->p("Your photo $filename:"),
  $query->img({src=>"../uploads/$filename",alt=>''}),
  $query->end_html;

(MY HOST and MYWEBSITE changed to protect the innocent!)

Thanks in advance
SF

nothing obvious i can see.
has your image file been uploaded and written to /upload/ ?
(btw your src attribute value says /uploads/)

if all else fails, try simplifying your script to see if something else happened without leaving clues:

use strict;
use warnings;
use CGI;
use CGI::Carp qw/fatalsToBrowser/;

my $query = new CGI;

my $file = $query->param("photo");
my $email_address = $query->param("email_address");

print $query->header(),
$query->start_html(-title=>'CGI Script Testing'),
$query->p("Your email address: $email_address"),
$query->p("Your photo file: $file"),
$query->end_html;

also:

my ($filename,undef,$ext) = fileparse($file,qr{\..*});

that pattern for the file suffix is "greedy and promiscuous" [google.com] so if your file name is file.name.ext then the suffix is .name.ext which means name could be almost anything and you should be careful what you do with $ext - i would suggest using a less ambiguous pattern such as qr/\.[^.]*$/

No file was uploaded - the browser went blank and the name and path of the script appeared in the address bar.

when you execute the script from the command line what is the output you get?
try putting the print $query->header(); immediately after creating the CGI object.

what are the permissions and ownership of the upload(s) directory?
i would add "or warn" or "or die" as appropriate after all system calls especially i/o.

I can't see anything from the log files really indicating what is wrong!

but you can see the POST request to the ACTION= script from your form submit?
and it is showing a 200 response code?

No file was uploaded - the browser went blank

that is why i would start with a simple print "hello, world!"; script and then see if you can retrieve parameters as i suggested above and then see if you can get a file.

the name and path of the script appeared in the address bar.

this is expected behavior.
you presumably got a response from the server.
have you tried "view source" from the "blank" page?

a tool such as the "LiveHTTPHeaders" [livehttpheaders.mozdev.org] add-on for firefox can be helpful in debugging cases like this.

Phranque

Thanks very much for all the tips - I went back to basics and started with a 'hello world' script which worked - then executed it via an html page.

In looking at the previous log files, they didn't show up any POST requests being sent. I re-uploaded the files using my own FTP (rather than the on-site uploader) and believe this may have done the trick. Although the 'uploader' assured me it had uploaded the scripts in binary - I'm not convinced. Anyway I now seem to have the scripts functioning - not necessarily correctly but functioning all the same!
Thanks very much for your help!

Is the upload directory writable?