Oracle – Cannot Find Order Entry Folder in $ORACLE_HOME/demo/schema/

Sounds like you don't have SELECT access on the sequence. Ask the DBA to run:

GRANT SELECT ON SCHEMA_OWNER.MY_SEQ TO APP_USER;

Can you edit your post with the full error message you're receiving?

Regarding your comment. I suspect you've got SELECT ANY TABLE etc privs. These don't apply to sequences, as demonstrated below:

PHIL@PHILL11G2 > create user test1 identified by test1;

User created.

PHIL@PHILL11G2 > grant connect,select any table to test1;

Grant succeeded.

PHIL@PHILL11G2 > create sequence testseq;

Sequence created.

PHIL@PHILL11G2 > conn test1/test1;
Connected.
Loading glogin.sql

Session altered.

TEST1@PHILL11G2 > select count(*) from phil.bigtable;

  COUNT(*)
----------
   2300640

TEST1@PHILL11G2 > 

TEST1@PHILL11G2 > select phil.testseq.nextval from dual;
select phil.testseq.nextval from dual
            *
ERROR at line 1:
ORA-01031: insufficient privileges

A logical schema won't exist in your database. A logical schema is a design-centric database structure built to meet your business requirements. It is a model that exists on a white board or in a diagraming tool. It is like the architect's drawings of your database.

A physical model is what is actually implemented in your DBMS.

The two can be different for a variety of reasons and in several ways:

• Your logical model should be properly normalized, but your physical model may have denormalization which you've added deliberately and for all the right reasons.

• Your physical model may have different naming conventions. Some people use plain English (or the language of choice) for their logical models and impose a more "system-ish" naming convention in their physical model.

• Your logical model may have many-to-many relationships. Physical models implement m:n using intersection tables.

• Your logical model may only use natural or business keys. Physical models may also add surrogate keys.

You should have a logical model because it lets you think about your database design without having to get bogged down in physical constraints. You need to have the physical model because that will be where your data eventually lives.