Frequently get "The backup disk image “/Volumes/TimeMachine/MyMBPro.sparsebundle” is already in use" message
Do you have access to you Western Digital MyBookLive via ssh ?
Can you change some config files from it?

I believe Western Digital MyBookLive use netatalk for allow connect to it via afp protocol from mac os x.
If it is true, when you abnormally disconnect from you MyBookLive netatalk wait by default 24 hours before dropping you connection see disconnect time parameter.

If you have access via ssh to you MyBookLive you can add "disconnect time = 1" parameter (one hour before dropping you connection) to the afp.conf file

And you can set "sleep time = 1" (Keep sleeping AFP sessions for number hours before disconnecting clients in sleep mode. Default is 10 hours.)

If you don't have access via ssh. I don't now. Maybe need check new firmware for you device, contact WD technical support on this issue.