New Message: Outgoing trackback problem

[webmaster at userland.com]

A new message was posted:

Address: http://manila.userland.com/discuss/msgReader$1399

By: Matt Deatherage (frontier at gcsf.com)

How do we debug outgoing trackback problems?

When I post a news item that references this page:

http://www.washingtonmonthly.com/archives/individual/2005_10/007392.php

..the site never gets the trackback ping, or at least never registers it. I have the above URL in the news item, and I found the explicit TrackBack ping URL in the page's source and added it to the news item's "URLs to Ping" field. Neither seems to have worked. The message's trackback table seems to indicate that a ping was sent, but I can't make heads or tails of the specifics.

What is failing there, and how could I have diagnosed it on my own?

This is a Manila site... http://manila.userland.com/.