"ORA-28001: the password has expired" not fixable

Can you post the results of the following? Also, what version of Oracle are you using? I'm assuming 11G?

select * 
  from dba_users 
 where username = '<yourUserName>'

select p.* 
  from dba_users u
     , dba_profiles p 
 where u.profile = p.profile 
   and u.userName = '<yourUserName>'

I'd be curious to see what profile you're using, and what your settings are.

I am 100% sure that my config is correct. I was overwriting all local data with the files from the productive app server. Still no success.

The problem is also this password expiry problem came suddenly while developing, so I am sure that I did not change anything.

However, I logged into the test system and reset the password there. My test system contains like 100 rows, my productive app like 1 million, so I can definitely tell you that I am on the right database.

After resetting the password of the test system, I can log-in again! So this whole story is very strange. Thanks for the support.

Assuming the Oracle DB (should work for Oracle-XE's SAMPLE as well) is on Unix, ssh-in and :

sqlplus /nolog

SQL> connect / as SYSDBA
Connected.

SQL> SELECT username, account_status FROM dba_users WHERE ACCOUNT_STATUS LIKE '%EXPIRED%';
# ... your locked account should be listed ...

SQL> ALTER USER sample IDENTIFIED BY sample;         
User altered.

SQL> ALTER USER sample ACCOUNT UNLOCK;
User altered.

SQL> ALTER PROFILE DEFAULT LIMIT PASSWORD_LIFE_TIME UNLIMITED;
Profile altered.

SQL> exit