Go to the Netflix website and click on "Your account & help".
Under Instant Watching, click on "Manage devices & computers".
Next, disconnect your devices*.
After that, try to enter the Netflix app on the Tivo and see what happens.
* Note this will disconnect all of your devices, so you will have to re-activate each one individually.
The idea here is that there could be something awry with the connection between the Tivo and Netflix, and doing this might flush the system (so to speak).
The Man Prayer: I'm a man ...... I can change ...... If I have to ...... I guess.