Once upon a time i faced an error ORA-02304 while Importing one database schema to another user (Actually i was copying the scheme for some reasons and i had already 1 copy of the same schema in my database).
The complete error was
IMP-00003: ORACLE error 2304 encountered ORA-02304: invalid object identifier literal IMP-00063: Warning: Skipping table "DEV_SCHEMA"."SUPPLIER_PAYMENT" because object type "DEV_SCHEMA"."SUP_PAYMENT_TYPE" cannot be created or has different identifier
Whenever you create Oracle object types with command for example
create type mytype as object (ids number, names varchar2(60));
Oracle assigns Object ID internally for all objects while i was imported the same Type with Same Object ID was already exists in my database.
One column in my table SUPPLIER_PAYMENT contains Nested Table type column and in my database i had already one copy of my schema and NESTED TABLE TYPE with same Object ID (Internally) named SUP_PAYMENT_TYPE.
Whenever you create objects with TYPES its a good practice to create all objects types in separate schema so you can share your objects in different schema's objects.
I removed the duplicate schema from the database and re-imported my tables and everything went smoothly.
So, Keep in mind If u going to work with objects in Oracle its better to create them in separate schema.
Have a nice day,