I just went to check in for my flight tomorrow, DAY-ORD-MCO, and I wanted to standby for an earlier DAY-ORD, which appears to have plenty of seats, H9. But, after I click the "standby" icon, I get the message "There are no standby flights available." This is not so, and the flight I want is not closed out, what gives?

ADDED:
I just wanted regular standy, I don't want the confirmed fe based standby option. Also, I am not within 3 hrs of my scheduled flight. Does that matter for the "free" standby option?