ORA-1017 after DB upgrade to 12cR2

Symptoms:

After db upgrade to 12cR2 user log in fails with ORA-1017.

Cause:

This is due to sec_case_sensitive_logon set to false. sec_case_sensitive_logon parameter is set to true by default in release 12 and users with password version below 12 are unable to login

Solution:

To fix this remove the deprecated instance initialization parameter sec_case_sensitive_logon  or set it to true. To support password version below 12 add the below parameter in sqlnet.ora of db home.

SQLNET.ALLOWED_LOGON_VERSION_SERVER=11