There is a difference between how you are running the command and how the webserver does (as evidenced by the fact that the webserver produces an error). Figure out what that difference is and you are more than half-way to solving your problem.

Erm... I have run it from the web server account=="nobody".

Any other ideas?

You didn't fully implement my first one.

Same user and same environment!

If it is running as a CGI command, it is being passed a lot of information in %ENV. Try changing the code that has trouble to something like this:

#! /usr/bin/perl
use Data::Dumper;
print "text/plain\n\n";
print Dumper \%ENV;
[download]

That gives you the environment. Do a bunch of export foo=bar to set up that environment and see what happens when you run this offline.

There is a difference between what you are executing and what the webserver does. You need to track that down.