WordPress doesn't do what it says
Tinderbox can't GetRecentPosts from your WordPress weblog, because WordPress fails to implement the GetRecentPostTitles API.
That's a problem, because, without it, most servers will only let you retrieve a few recent posts. When you ask for a lot, your server runs out of memory and gives up.
I'm sure this is just an oversight, and that the WP folks will fix the bug soon.