invalid national character set specified

Try the following links for this error:

http://docs.oracle.com/cd/E16655_01/server.121/e26079/e12700.htm

https://community.oracle.com/message/4577872

https://community.oracle.com/message/3780743

https://community.oracle.com/message/1858937

https://community.oracle.com/message/3780437

https://community.oracle.com/message/773315

https://community.oracle.com/message/2621222

https://community.oracle.com/message/3403575

https://community.oracle.com/message/731087

https://community.oracle.com/message/9502614

https://community.oracle.com/message/977055

https://community.oracle.com/message/687387

https://community.oracle.com/message/1845863

https://community.oracle.com/message/9760796

https://community.oracle.com/message/3889287

https://community.oracle.com/message/2628091

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