You can’t format the MBW because it’s a network drive, not USB. It uses a Linux file system called EXT3 to make it work over the network using SMB all systems. TM compatibility with the drive is firmware-based, not FS-based.
If you are using a blue rings MBW and your Mac is using a recent version of OSX like 10.8 or 10.9 then you’re out of luck. if you have the white light MBW then I don’t know if WD made an update to make it work with 10.9 since they have that drive on their legacy page.
