An Oracle7 to Oracle8 convert file contains invalid data or was created with an different version of the migration utility. This error can also be caused by incorrect ORACLE_HOME environment variable when ALTER DATABASE CONVERT command is issued.
Use a correct version of the convert file or regenerate it with the migration utility. Make sure that the migration utility is the same version as the Oracle8 RDBMS executable and that the ORACLE_HOME environment variable is properly set.
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Try the following links for this error:
http://docs.oracle.com/cd/E16655_01/server.121/e26079/e0.htm