If you're using a Mac and you're getting error C:1501 (like I have been today!), there's some useful stuff here:

Doc’s Tech Notes: Fix Netflix error code 8156-6013 on a Mac

I had removed and re-installed Silverlight but that didn't fix it. I found the above page, which is about a similar problem with Netflix. In particular, the step "Remove the Silverlight DRM file" seemed to fix it for me.

Hope it helps someone...