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ORA-01240:

too many data files to add in one command
Cause: The command specifies adding more data files than can be done in one command. It is necessary to fit all the file names into one log entry, but that would make the entry too large.
Action: If this is a CREATE TABLESPACE command, create with fewer files then add the other files later. If this is an ADD DATAFILE command, break it up into multiple commands.