In this link How to recreate public synonym "DUAL"? I've the same problem with one diference.
I executed this comand: CREATE OR REPLACE PUBLIC SYNONYM "DUAL" FOR "DUAL"
CREATING SO A "LOOPING CHAIN OF SYNONYMS". SO A REMOVE THE SYNONYM.
NOW MY PROBLEMA IS: The SCHEMA "exemple" can't connect in DUAL. (select * from dual) only can doing (select * from sys.dual).
We are trying to recreting the SYNONYMS but nothing are working. Someone can help me?