EM 12c : Unable Login To Target Database " ORA-01017: invalid username/password; logon denied " Error Returned (Doc ID 1521695.1)

Symptoms

From EM 12c Console, unable to login to target Database when performing any administration task.
When entering SYS credentials (SYS username and password), the following error is returned :
 ORA-01017: invalid username/password; logon denied

Solution

Check the following :
1. The following database parameter should be set either to SHARED or EXCLUSIVE and not NONE :

remote_login_passwordfile=EXCLUSIVE

2. On Windows, Set the following Sqlnet parameter in <ORACLE_HOME>/network/admin/sqlnet.ora file:

SQLNET.AUTHENTICATION_SERVICES=(NTS)

On Unix, ensure that this parameter has the correct value by referring the two documents that are mentionned below in REFERENCES section.
3. Test the Remote Client/Server database connection using Sqlplus installed within the OMS Oracle_Home.
3.1 Using TNS alias defined under <OMS_ORACLE_HOME>/network/admin/tnsnames.ora file
This Remote Client/Server Connection database Test should successfully work.

cd <OMS_Oracle_Home>/bin
sqlplus /nolog

connect sys/<password>@<tns_alias> as sysdba
=> replace <tns_alias> with the alias tns defined under <OMS_ORACLE_HOME>/bin and that points to the target database

3.2 Using the complete NET connection string.
This Remote Client/Server database Connection Test should successfully work.

sqlplus /nolog

connect sys/<password>@'(DESCRIPTION=(ADDRESS_LIST=(ADDRESS=(PROTOCOL=TCP)(HOST=<hostname>)(PORT=<port>)))(CONNECT_DATA=(SERVICE_NAME=<service_name>)))' as sysdba
=> Replace <Hostname>, <port>, <service_name>, with the appropriate values that correspond to the impacted target database.

Contact the database's administrator to investigate any error returned when testing it.
Refer as well the two references notes mentionned in the "REFERENCES" section.
3.3 The error returned by either of the two previous tests described in 3.1 and 3.2, will help to troubleshoot and fix the remote client/server connection
between the OMS and the target database.
A classical error that could happen by testing the sqlplus connection is :
ORA-01031: insufficient privileges
That means, that :
either
The password file of the target database would be corrupted or incorrect.
Or
The password file has the different password setting.
Contact the database's administrator to investigate this error, and to re-create the password file only if required/needed.
For this error, and all other errors, Refer the two references notes mentionned below to help to diagnose, and fix the remote client/server database connection error.

REFERENCES :
Two notes can help to troubleshoot the Client/Server Database connections
Document 730067.1 Troubleshooting ORA-1031: Insufficient Privileges While Connecting As SYSDBA
Document 233223.1 Checklist for Resolving CONNECT AS SYSDBA (INTERNAL) Issues

4. As soon as the remote client/server connection is working fine in either of the two tests described in 3.1 and 3.2, go back in the EM Console to try again to login to the target database from
the database home page for instance, or when performaing any administrative task, or when creating/testing database credentials

Thanks
Srini