I'm having the same problem.
I tried reinstalling the Netflix plugin to no avail. Tried installing a couple different versions of Silverlight which didn't make a difference.
I called Netflix and they suggested reinstalling WMC. I tried, but all I was able to do was disable WMC, reboot, and then reenable it. When I reenabled, all my settings came back, so I doubt that helped.
Has anyone else tried contacting Netflix Tech Support? I'm assuming the more calls they get, the more likely the issue will get fixed.