I just wanted to let the WD support know that I have exactly the same issue with my few month old WD Mybook Live!!!
No chance to access http://mybooklive/UI anymore - not by its name nor ip address.
Just like @jstrathman I have configured everything right and was also successfully using the WD2Go app on my iPhone to access the drive.
Since the latest firmware update yesterday the drive is bricked now - thank you WD!!!
Although I can still access all data on it and I can also access http://MBL/UI/learn_center/learn_main/de_DE
What can I do other than have it replaced with a “refurbished” one?! 
