PostgreSQL user can not connect to server after changing password

Question

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?

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