Can't book more than 2 nights

[Mark-N-Coreen0]

When I try to check availability, I can only enter a 2 night duration. Anything more shows not available. Yet, if I move the dates ahead a day, 2 nights are avaialbe. So I should be able to do a 3 or 4 night span on the calendar, but no go. 2 nights comes up, but anything more, though it looks available, doesn't let me continue. Am I doing something wrong?

First time user.