This error occurs when you have a public synonym defined and the object referencing or owning the synonym has been dropped or deleted. You can check for the invalid synonyms using below query.
select * from dba_synonyms s where table_owner not in('SYSTEM','SYS') and db_link is null and not exists (select 1 from dba_objects o where s.table_owner=o.owner and s.table_name=o.object_name);
Replace the synonym with the name of the object it references or re- create the synonym so that it refers to a valid table, view, or synonym.
The Invalid synonyms must be dropped and recreated with the right owner. I normally do this using below query.(In this example the owner of the synonym was dropped and I am altering the synonym to reference the new owner)
DROP PUBLIC SYNONYM SYNONYM_NAME; CREATE PUBLIC SYNONYM SYNONYM_NAME FOR NEW_OWNER.OBJECT_NAME;