"An unknown error occurred" when signing in password to my Apple ID

Hey guys! I have been bothered about this pop-up message on my MacBook Air. I am trying to log-in to enter my Apple ID password but I keep getting this message over and over again. The message is "An unknown error occurred"... even though I have changed my password for the nth times and when I log back in I still get the same error message. I am running out of patience and about to throw my laptop out of the window now. If anyone can help me with this please let me know what I can do to fix this issue. Thanks much!