The real reason that you got this message is because you entered date for a weekday and not a Sunday, Solemnity, or Feastday. The "Go to a Reading by Date" ONLY works for Sundays, Solemnities, and Feastdays.
This message could be worded better because it gives you the impression that they have the DEMO text when in fact you actually do have the full product. What the message was trying to say is that given the date you entered, the readings could not be found and one possible reason might be that you have the DEMO text.