ORA-25176: storage specification not permitted for primary key

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This error message can be returned when an unexpected clause is added in a primary constraint specification for an index organized table:

CREATE TABLE test_table (
key_a varchar2(10),
key_b number(5,0),
key_c number(10,0),
col_d varchar2(30),
PRIMARY KEY (key_a, key_b, key_c) USING INDEX COMPRESS
) ORGANIZATION INDEX
/

ORA-25176: storage specification not permitted for primary key

Two facts must be noted here:
the "USING INDEX" clause above becomes perfectly legitimate if we remove the COMPRESS keyword or if we move it after the ORGANIZATION INDEX clause, as already explained in a similar situation occurring in Oracle XE, where a different error message is returned (see ORA-14071).
Likewise, if you remove ORGANIZATION INDEX, the COMPRESS clause will be accepted without problems:

CREATE TABLE test_table (
key_a varchar2(10),
key_b number(5,0),
key_c number(10,0),
col_d varchar2(30),
constraint pk_test_table primary key(key_a, key_b, key_c) USING INDEX COMPRESS 2
)

In conclusion, you just picked a wrong syntax, if you want to enable compression on an index organized table, then change the statement as follows:

CREATE TABLE test_table (
key_a varchar2(10),
key_b number(5,0),
key_c number(10,0),
col_d varchar2(30),
PRIMARY KEY (key_a, key_b, key_c) USING INDEX
) ORGANIZATION INDEX
COMPRESS -- see the note below
/

As already mentioned in a previous posting, you can also specify COMPRESS n, where n is a number lesser than the number of key columns and in this specific case you could specify either COMPRESS 1 or COMPRESS 2, because the key is made up of three columns.
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