Oracle Error Message
ORA-38863: datafile string has been restored from an optimized RMAN backup.
Reason for the Error
Flashback Database could not flash back the file because it was restored from an RMAN optimized backup with deallocated objects. Flashback cannot revert the file to a time before the last deallocation in the datafile backup.
Solution
Restore the file from a backup prior to the Flashback target SCN or time and then retry the command.