Just a little bit of extra forum advice - rather than create multiple replies, you have a short time after posting to edit - in the top-right of your post, click "post options" and "edit post".
Second up, as I alluded to previously - both TiVo & V6 boxes both run TiVo software but thanks for confirming they are V6 - and that subtly changes the advice I'll offer. Can both V6 use OnDemand reliably? The connection between the V6 & your homehub is the same for both services, so this is a good test.
Have you tried restarting each V6 in turn? You can do so via the menu under Home > Help & Settings > Clear or restart.
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