Man, this just reminds me that I received a Project Spark beta key but can't use it because my Windows 8.1 installation refuses to let me use any games that require signing into Xbox Live first. Extremely frustrating, and I've tried tons of different fixes. Apparently Microsoft has no idea what's going on either, since there are other people out there with the same problem and the only response I've seen is "It's an issue on our end and we're looking into what's causing it" from a few months back.