When you want to use your WD-MyBookWorld as a Time Machine Backup, you'll probably get this error: The operation couldn’t be completed. (OSStatus error 2.)
To fix it, you have to login with your WD_Backup User.
Go to your MyBook World Website (via Bounjour) and go to "Users". You'll see the the "WD_Backup"-User. Set your own password and use this login data in your Mac Time Machine.