There appear to be lots of problems with posting to Facebook lately. If you try the full reconnect procedure detailed at http://en.support.wordpress.com/publicize/#reconnecting-facebook including step 3 (removing the FB app), which is probably the most important step and it's not successful there are 2 alternatives aside from manually posting.
Alternatively you can use Networked Blogs http://www.networkedblogs.com/ or RSS Grafitti http://www.facebook.com/RSS.Graffiti for posting to Facebook walls if you prefer. RSS Graffiti periodically checks the RSS/Atom feeds that you specify and posts any new entries it finds to the Facebook Walls that you specify. You can get any feed written on any wall (Facebook Profiles, Fan Pages, Groups, Events and Application Profile Pages). In fact, multiple feeds to multiple walls. You choose the combination.