SQL & PL/SQL :: Accessing Dmp Via External Table

when i am writing dump from external table, it is accessing records from dump.but when i am trying to access other dumps(create thru expdp) it is giving error.the logic i am following is mentioned below-

CREATE OR REPLACE DIRECTORY "DIR_GMS" AS 'D:Gopal_works est_env_files'

GRANT READ ON DIRECTORY dir_gms TO gopal;
GRANT WRITE ON DIRECTORY dir_gms TO gopal;

-- creating dump file in directory

CREATE TABLE emp_ext
ORGANIZATION EXTERNAL
(
TYPE ORACLE_DATAPUMP
DEFAULT DIRECTORY dir_gms
LOCATION ('emp_ext_dmp.dmp')
)
[code]......

i am able to see records.

New point:
-- taking export thru expdb
expdp hr/hr tables=EMPLOYEES directory=DIR_GMS dumpfile=HR_EMP.dmp logfile=expdpEMP.log
then i created one EXTERNAL TABLE TO access it.

CREATE TABLE emp_xt (
EMPLOYEE_ID NUMBER(5),
FIRST_NAME VARCHAR2(50),
LAST_NAME VARCHAR2(50))
ORGANIZATION EXTERNAL (
TYPE ORACLE_DATAPUMP
DEFAULT DIRECTORY dir_gms
LOCATION ('HR_EMP.DMP')
);

while accessing, it is giving error:

SELECT * FROM EMP_XT

ORA-29913: error IN executing ODCIEXTTABLEOPEN callout
ORA-31619: invalid DUMP FILE "D:Gopal_works est_env_filesHR_EMP.DMP"
ORA-06512: AT "SYS.ORACLE_DATAPUMP", line 19