The backup application cannot read the tape. Block 10 is where I would expect the Filemark which designates the beginning of the first session should be.
the backup was done via a different application
the tape has been erased or corrupted
Try reading another backup from the same set or close to the same point in time. This is to find out if the problem is just with this tape or all tapes.
If it is just this tape that cannot be read then there is always data recovery.