Note: Run SQL below as SYS (connect as sysdba)
Are there any invalid objects?

select owner,object_type,object_name from dba_objects where status != 'VALID' order by owner, object_type;

Rebuild all invalid PACKAGE/PACKAGE BODY etc.

exec UTL_RECOMP.RECOMP_SERIAL ();

Are there any bad indices?

select owner, index_name from dba_indexes where status like 'UN%';