Under System Information:
When was the last successful:
TiVo Service connection?
GC (Garbage Collection)?
You might have to pull the (signal source) coax for long enough to free up enough resources to let all of these complete. If you have a tuning adapter, they sometimes need to have their power pulled off long enough to let all these complete.
Try Clear Program Information and To Do List (with coax disconnected), and see if they all complete.
If all that fails, intentionally use zip code 00000 for guided setup, use "Tiny TiVo" as your provider, keeping coax disconnected, preferably, let all the things in the list complete, then use the correct zip code and provider, not connecting the coax until all have completed, and the guide data is full.