Please consult Common Reasons Why a Post Failed to Publicize
Post the snippet and link manually To Facebook to save time first and then proceed as follows.
1. Try flushing your FB cache but disconnect from FB first http://umairj.com/146/how-to-clear-facebook-shares-cache/
2. Try the full reconnect procedure again detailed at http://en.support.wordpress.com/publicize/#reconnecting-services
Note: RSS Grafitti http://www.facebook.com/RSS.Graffiti can be used 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.
Please note that reconnecting Publicize with Facebook and/or with Twitter does not re-publicize missed posts, but it will work for future posts.