I am seeing the above error on my TiVo box. I also have a V6 box that appears to work just fine. While the N26 error is there, I can see that the TiVo is actually getting a DHCP address, however it seems to be missing DNS and IP address for the gateway, which I suspect is why it is failing.
I've plugged other devices into the cable and they all work as expected (connect to the internet and get a DNS and gateway IP).
OK, this has been resolved - the issue was not the local LAN setup at all. The issue was the Virgin Cable to the box. Once this was resolved, everything started to click back into place.
There were some strange anomalies, such as the fact the system reported that it had not connected since 13th March, but the box had been used to watch TV up to the 26th March, so unsure why the confusion there, but at least it was an easy fix!