This seems to be a real thorn in some people's paw. Like mine, for instance, lol.
I cannot stream tracks in Napster. Walking through some troubleshooting steps with the nice Napster folks got us to the streaming proxy settings in WMP11 - Tools/Options/Network tab.
They wanted me to edit the protocol settings for the items in the "Streaming proxy settings" list. When I told them I had nothing in that list, they said, "well there it is! But we cannot help you because we don't know how to get protocols into the list. We do know that's the problem, though, and you'll have to talk to Microsoft about it."
Apparently, no one else knows how to get anything into that list either, or how they might go away in the first place.
If anyone has come across this issue and found the resolution, I'd be eternally grateful.