If you are unable to post to Facebook, go through this checklist:
1. Ensure the latest version of BikeBrain is installed.
2. Go to Settings > Sharing Settings and sign out of Facebook and then sign in to Facebook again. Then share a trip again.
3. If you use iOS 6 or above, go to iOS settings > Facebook > BikeBrain (off) > close settings. And then go back to iOS settings > Facebook > BikeBrain (on).