We had the same issue and were able to fix it. If you have ever moved and transferred your Xfinity service to a new address, this is happening most likely because your XFinity account is still linked to an old address and that address is still designated as your "primary account." I know this probably makes no sense, but whatever is listed as your Primary Account is what the Smart TV Xfinity Beta App tries to connect to. You can call customer service and ask them to unlink the old account (it says you can change your primary account designation through your online account management/details, but this didn't work for us). Once they did that, we deleted the app from our Smart TV, reinstalled it, and viola... worked like a charm and didn't mess up anything with our account.
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