This one threw me for a while and I could find nothing specific on the web. I wanted to use my Xbox 360 to watch video streamed from my Windows Home Server. Streaming is switched on by default, I hear you say. Why, yes it is, but each time I tried to connect the Xbox I received an error.
The solution? Enable the Guest account on the server. Do this with care – revoke it’s access to everything except the folders you want to stream unless you want to allow read access to everything on the server.
Once Guest was enabled and the access rights were applied the whole thing worked like a charm.