Trackback and pingback broken – WP2.0.4

My test/dev install works just fine and is an exact replica of prod, but I am unable to get track and pingbacks of any description working on my prod install at https://www.stephencollins.org/

I am reasonably certain that xmlrpc.php is responsible (e.g. Flickr calls my xmlrpc.php URL an invalid endpoint), but I can’t get at my logs from work to check…

I am on a host that provides the following:
Apache 2.0.52
PHP 4.3.9
MySQL 4.1.12

I know in the past that it’s worked, and I’ve tried pretty much everything I can to make it happen.

Any advice on the right way to test this will be appreciated greatly.

If anyone needs to see my PHP environment, I can email you a URL to do so.