Either the username does not exist in the database or the password is invalid.
To check which users exist in the database, use following select:
select username from all_users
If you want to have logging of all invalid attempts, enable database auditing by setting the value of the database parameter audit_trail to DB.
Also enable auditing for invalid connections by using following statement:
audit create session
After that, you can find useful information by querying the dba_audit_session data dictionary view:
select * from dba_audit_session where username='MYUSER' and returncode != 0;
If you do not need auditing anymore, you can disable it with following command:
noaudit create session;
As of Oracle version 11g, the database administrator has the ability to specify that a password is case sensitive. Before Oracle 11g, the case didn’t matter.
If database parameter sec_case_sensitive_logon is set to TRUE, you will need to make sure that the password provided is in the correct case.
You can use our free tool Oracle Password Changer to change the password of an Oracle database user.