Oracle Error Message
ORA-38704: Checksum error in flashback database log file header.
Reason for the Error
The flashback database log file header contained a checksum that does not match the value calculated from the file header as read from disk. This means the file header was corrupt.
Solution
If you are doing a FLASHBACK DATABASE, then the flashback cannot be performed because of the corrupted log. A restore and an incomplete recovery must be performed instead.