I've been fighting with a strange error when trying to sign-in a test user on the Xbox (see error message below). I have two users assigned to my test Xbox console. I've set the sandbox ID correctly (and added that Sandbox ID to my Xbox in Dev Mode). I've added <uap:SupportedUsers>multiple</uap:SupportedUsers> to my Package.appxmanifest file. Is there anything I'm missing? I have done a good bit of debugging in Microsoft.Xbox.Services.Client.SignInManager class. When the game launches, the Xbox opens the side-bar dialog with a list of all the test users on the console. I choose one, and SignInManager tries to run playerInfo.XboxLiveUser.SignInSilentlyAsync(). That returns a status of UserInteractionRequired. After seeing that status, SignInAsync() is called. The Xbox puts up a dialog for a moment, and then it closes, and that's when I get this exception: XboxException: Xbox Services flat C API return error code -1000 with message "Provider Error: Unexpected response code: Unknown error: 0x80131509" Does anyone know what that means? The processing of the sign-in bails when that exception is thrown. I'm sure it's one little thing I'm doing wrong, but it's hard to know what it is. Also, I had trouble finding a good forum on any of Microsoft's sites to post this...if you guys feel this post belongs there, please feel free to send me a link to the proper forum. Thanks, all!