I've met this with 4 roles I created:  
After changing password for a user in pgAdmin III using the GUI (1), that user can not log in any more.  
pgAdmin III show error message:

    An error has occurred:
    
    Error connecting to the server: FATAL:  password authentication failed for user "sam"
    FATAL:  password authentication failed for user "sam"

My system: Postgresql 9.2 on Ubuntu 12.04  

Is there any way to fix this?
Thanks.


(1): login with account postgres, right click user in Login Roles, go to tab 'Definition' and enter password