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ORA-01673:

data file string has not been identified
Cause: This data file was not in the control file after an incomplete recovery or CREATE CONTROLFILE. Since information from its header is needed for standby database recovery, we can not create a standby control file.
Action: Find the file and bring it online. If desired it may be taken offline again. If you intend to drop this file, then taking it offline with the DROP option will avoid this error.