Oracle recommends that the password entered should be at least string characters in length, contain at least 1 uppercase character, 1 lower case character and 1 digit [0-9].
Provide a password that conforms to the Oracle recommended standards.
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Try the following links for this error:
http://docs.oracle.com/cd/E16655_01/server.121/e26079/common_errormessages.htm
https://community.oracle.com/message/9567507
https://community.oracle.com/message/10191329
https://community.oracle.com/message/9752198
https://community.oracle.com/message/11157995
https://community.oracle.com/message/11115519
https://community.oracle.com/message/11270807