PostgreSQL user can not connect to server after changing password
It's possible that you're being bitten by this PgAdmin bug (changelog):


  2012-11-28 AV  1.16.1  Date picker controls returns a full timestamp
  by 
                         default, which can cause inadvertent date changes
                         on jobs and role validty dates. Ignore the time part.


This bug has been seen to set password expiry dates far in the past, such as 1/1/1970. In this case the error message when trying to connect is no different than with a wrong password.

You can check these expiry dates with:

SELECT usename,valuntil FROM pg_user;


and if they're wrong, reset them with:

ALTER USER username VALID UNTIL 'infinity';


and upgrade pgAdmin.