A couple of times, arbitrary rule-sets have been attached to blocks of dates on my calendar. Go to the date, scroll down, and make sure you have no rule-sets attached. On mine, it had set my maximum length of stay to 1 day. Since my minimum length of stay is 3 days, it blocked the date.
Even if this is not your problem, just a reminder that these days (well every day, really), it’s important to check your listings to make sure arbitrary glitches such as this aren’t affecting them.