Here at the SAT GE office it happens all the time. One day there'll be none and you get the same message you've pasted then the next day a whole month's worth will show as available. I think I started out with no appointments listed then a few several weeks out and finally a number just a week away. My wife decided to enroll a couple of months later and went through pretty much the same drill. We followed the recommendations here and just kept checking and actually got our interviews done within a couple of weeks of our conditional approvals.