Run this script to have a look at your environment:

#!/usr/bin/perl -wT
use strict;
print "Content-type: text/html\n\n";
print "<p><b>$_</b><br>$ENV{$_}\n" for sort keys %ENV;
[download]

What I expect you will find is the REMOTE_ADDR contains a value but REMOTE_HOST does not. This occurs because reverse DNS lookups need to be enabled on the server to allow your server to convert REMOTE_ADDR into a hostname.

You should be able to convert REMOTE_ADDR into a hostname yourself using gethostbyaddr():

use Socket;
$iaddr  = gethostbyname('www.perlmonks.com');
$name   = gethostbyaddr($iaddr, AF_INET);
print $name;
[download]

cheers

tachyon

s&&rsenoyhcatreve&&&s&n.+t&"$'$`$\"$\&"&ee&&y&srve&&d&&print

REMOTE_HOST is usually set by the Web Server
For example, from Apache HostName LookUps

So you will need to be aware of the change in web server configuration.
There is an outside chance that if you have moved machines that the DNS is different and the lookup is failing. But that is not so likely.

As busunsl stated, more details are required.

<a href="http://www.graq.co.uk">Graq</a>

Tell us a bit more about the environment:

Server, OS, Versions of all, etc.