Loading External Table from dumpfile
If you look up the description of error ORA-39324 in the Oracle documentation you will see:

Cause: A dump file was specified for a load operation that had been created using the Data Pump. This type of dump file cannot be processed by external tables using the ORACLE_DATAPUMP access driver.
Action: Access the data in this dump file using the Data Pump.

A dump created by EXPDP can only be read by IMPDP (or dbms_datapump).  Whereas a dump created using writable external tables (using datapump driver) can be re-read only using external table interface (using datapump driver). Expdp does more than dump data (which is the only thing done by writable external tables using datapump driver).

Community Wiki answer originally based on comments by BriteSponge and Raj

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