I just got a My Book Essential Edition 1TB external hard drive.
It came formatted for Windows with a FAT32 filesystem but as I’m on OS X I wanted to repartition and change the filesystem to Mac OS Extended (Journaled). Should be easy enough using Disk Utility but it just kept bitching about some error:
“The underlying task reported failure on exit.”
Useless. No information as to what actually went wrong. Looking in the system.log (/var/log/system.log) more information was revealed.
Disk Utility: newfs_hfs: /dev/rdisk1s1: partition size not a multiple of 4K.
So by changing the partitions to be a multiple of 4K everything now works.