Well, he may have posted in the wrong forum, but the problem he describes could happen to any WD Live unit, as it has happened to my Live Plus.
Suggest that the poster of the issue recall if he has installed anything new on his PC lately, because that caused my similar problem.
What I had installed was a newer version of the Pogoplug software, and knowing it was also a DLNA enabled program (the Pogoplug hardware and drive can serve media to the WD media player) I immediately suspected the new software. So, I turned if off and the WMP “play to” feature worked again. I turned the Pogoplug software back on and “play to” quit working again. Solution found: turn off the Pogoplug software when I want to use WMP and “play to”.
Yep, an inconvenience I could do without, but at least I found the source of the problem. I need to write to Pogoplug and let them know about this issue.
Another idea: the poster could have added another DLNA hardware and that could be the cause. Otherwise, I haven’t any other ideas of what the cause could be.