Cause: NCLOB, NCHAR or NVARCHAR2 data changed the representation to Unicode when converting to a multibyte character set and must be migrated. See the solution below.
Error solution: Remove NCLOB, NCHAR or NVARCHAR2 data as listed in the alert file. The above type data can be migrated by methods such as import/export.
Database version: Oracle 11g Release 2 (11.2)