While investigating the feed import problem, I’ve noticed that feedvalidator.org throws an error with the generated wordpress rss2 feed. One easy fix is to change the following line in wp-rss2.php
from:
header(’Content-type: text/xml’, true);
to:
header(’Content-type: application/xml’, true);

Update: There is another issue with Wordpress and the validator, most wordpress feeds don’t validate due to this error message: Response includes bad HTTP header name: “last modified”
Apparently this can be fixed through upgrading to the latest version of Wordpress, 1.2.2.