Existing CDB public synonym get error on preupgrade tool (upgrade to 12.1.0.2)

@preupgrd

My experience of upgrade from 11.2.0.4 to 12.1.0.2 with one database was not successful at the beginning.

I have tried to execute preupgrd.sql as it was explained in documentation and Note 1503653.1, later downloaded preupgrade tool  and catch the same errors:

SQL>@preupgrd.sql

Loading Pre-Upgrade Package...

DECLARE

*

ERROR at line 1:

ORA-06553: PLS-221: 'CDB' is not a procedure or is undefined

ORA-06512: at "SYS.DBMS_PREUP", line 12458

ORA-06512: at "SYS.DBMS_PREUP", line 3214

ORA-06512: at "SYS.DBMS_PREUP", line 3153

ORA-06512: at line 56

Investigation of DBMS_PREUP help me found out the reason of messages:

The database has PUBLIC synonym CDB on user's  package.