It sounds like the update bricked your drive for some reason. Power down the unit and see if the drive will boot if you take out disk A and move disk B into disk A’s slot then boot it up with the one drive in there. If it boots up, shut the unit down and put the other drive back in the empty slot and boot up and see if raid repairs the OS on the other drive. If still a no go…
If you know your away around a computer you can try to debrick the OS by following this guide
http://community.wdc.com/t5/My-Book-Live-Duo/GUIDE-Debrick-a-MyBookLive-DUO/td-p/544860
Otherwise I would return it to the retailer for replacement
