disable the "smart" features in the vizio if you don't use them. You should also be able to enter the smart feature configuration menu and disconnect from the MTH network.
The only networks i can bring up are MTH and must be my neighbor judging by the strength of the signal. Since I'm only having the problem on 1 TV I'm guessing it's a problem unique to this TV. I've had the WiFi setup for 2 weeks and only had this problem show up yesterday. Even after I powered down the MTH unit it still shows as an option in the TV menu.