Here's your issue:
Jan 6 02:11:48 Tower unassigned.devices: Mount drive command: /sbin/mount -t 'hfsplus' -o force,rw,users,umask=000 '/dev/sdb1' '/mnt/disks/My_Book'
Jan 6 02:11:49 Tower kernel: hfsplus: Filesystem was not cleanly unmounted, running fsck.hfsplus is recommended. mounting read-only.