If your Facebook id has been blocked by a friend, you can still send him/her messages by following these simple
1. Login to your e-mail account ( example -gmail.com / yahoo.com).
2. Go to compose mail.
3. Enter the username of your friend as username@ facebook.com.(ex: example@ facebook.com)
4. Type-in the message(whatever you want to write) and then send it.
Your message will be in the inbox of the friend who has blocked you on
In this way you can regain the contact with your friends on Facebook and can resolve every issue.