If you want to change profile parameters, you have to use alter command. Default User Life Time coming limited as 180 in Oracle 11g. You can change of this limit. Because this parameter cause of expired password. If you do not want to expired password, You have to change this parameter.
Show Profile Parameters
SQL> SELECT profile, resource_name, limit FROM dba_profiles WHERE profile=’DEFAULT’;
Change Profile Parameters
SQL> ALTER PROFILE DEFAULT LIMIT PASSWORD_LIFE_TIME 60;
or
SQL> ALTER PROFILE DEFAULT LIMIT PASSWORD_LIFE_TIME UNLIMITED;