I am doing the same thing for last 24 hrs... It says

 

I had the same issue, very irritating. Exchanged my phone earlier today and it did not fix the problem. However I finally got it to work simply by just hitting try again, when it failed again, I would click try again, and eventually it worked.

 

I had exactly the same problem last night & eventually got it to login after repeated attempts but I logged out again today & have the same problem getting in again. Quite a few users are reporting the same issue on other forums but no sign of a cause or a fix other than persistence. Very frustrating.

 

After what seems like a thousand attempts, I'm finally back in.

 

This has been on before, I think it was decided that it was a Facebook problem and not the phone... Although this doesn't explain why you can log in elsewhere.