ORA-19660: some files in the backup set could not be verified
Cause: A restore conversation was made to verify all the files in a backup set, and the files which were printed in messages 19661 or 19662 could not be verified because corrupt blocks for those files were found in the backup set
Action: Unless the damage to the backup set can be repaired, the indicated files cannot be restored from this backup set
https://support.oracle.com/
http://www.oracle.com/