register_globals is off on the server where it isn't working.
WHS.
this one as you say is PHP Version 5.1.2 .. surely they'd be backward compatible though ?
As with MySQL 5 having strict mode on by default, several config options in PHP have had their default values changed for PHP 5. It's a lot more sensible now, but it can bugger up some scripts that were developed under 4's slightly more lax environment (I'm referring to the basic, unedited installation, naturally).
As
this says, you shouldn't really code with register_globals, as it can leave whacking great security holes if you're not careful.