In case this helps anyone else, here's some info that stumped me for a couple of months on how to get Xbox Live working in your game:
First off, remember to do the "NuGet" step shown under "Setting up Visual Studio" in this tutorial.
I also found that exporting to a fresh new folder instead of using the same one I always did helped. More accurately, I seem to have found that anytime I want to do a re-export out of C2 into the same directory, it breaks the Xbox Live functionality in the Visual Studio solution. I seem to have found that the easiest fix for this is to delete at least one if not all of these 4 files that Visual Studio creates:
Then I reopen VS and redo the NuGet step, Store Association step, and Visual Assets step.