Thanks for the very helpful reply

You could try putting this at the top of the script:

use CGI::Carp qw(set_die_handler);
BEGIN {
    sub handle_errors {
        my $msg = shift;
        print "Content-Type: text/html\n\n";
        print "$msg";
    }
    set_die_handler(\&handle_errors);
}
[download]

I'm going to write some test code so that I can properly test what is going on. It will probably have to wait until the weekend though. But this code has been a little confused!

Is set_die_handler a method of CGI::Carp and set_die_handler(\&handle_errors); in the BEGIN block is overriding it?
Or is something different happening here?