Welcome to Nokia discussions board!
I advise you to re-download the Facebook app from "my stuff" in Nokia Store. You may also send the app to your phone from the internet on a PC by clicking on this link.
Let us know how you get on and feel free to post any other questions you may have.
I have downloaded facebook app from http://store.ovi.com/content/238066.
After that i have tried to open this app, but still i am not able to connect it.