Here's an odd one. I used to write my blog entries for my multiple WordPress installs in Windows LiveWriter beta, but eventually switched to BlogDesk for its streamlined interface and speed.
Now I've got a new blogger working with me. He wanted to use LiveWriter, and damned if we couldn't get Windows LiveWriter working. He couldn't configure it, and I even downloaded the new version (which used all my old files and settings just fine), and I couldn't even get that to work with the same blogs it used to post to just fine.
Of course, in that six months since I ditched it, LiveWriter and Wordpress have both been upgraded, but honestly, both *should* work with each other (my blogger used the current version of LiveWriter with a Wordpress.com blog).
I get a "400" Error, and I've played around with the settings enough that I don't think I'm missing anything obvious.
Any ideas? Guesses? Communications from the dead?