Hiya,
Occasionally I have seen these messages flash up in the past, but not recently.
I was told that they were caused when switching from the slower 3rd tuner to another one of the 2 free ones on the tivo. - I don't believe it always stays on the same tuner when you change channels using the up down / channel number entry as opposed to changing via the info button when you choose the tuner and it obviously uses another tuner.
Am I rambling ?
"Space ... it's really rather big"
You may be suffering from this, or you may have other issues at play. Does anything else niggle you