Cause
When character set conversion happens between CHAR and NCHAR either implicitly or explicitly, some characters are lost due to no mapping characters in the destination character set.
When character set conversion happens between CHAR and NCHAR either implicitly or explicitly, some characters are lost due to no mapping characters in the destination character set.
Make sure all the characters can be mapped to destination character set or set NLS_NCHAR_CONV_EXCP to be FALSE.
Try the following links for this error:
http://docs.oracle.com/cd/E16655_01/server.121/e26079/e12700.htm
http://docs.oracle.com/cd/E16655_01/server.121/e17750/ch7progrunicode.htm
http://docs.oracle.com/cd/E16655_01/server.121/e26079/olap33k.htm
https://community.oracle.com/message/4266930
https://community.oracle.com/message/1483987
https://community.oracle.com/message/7422919
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