Originally Posted by asvs

From my experience with SFO this weekend, it just means that all the slots in the system have been claimed. You will be able to get back into the calendar if something opens up.

I was getting this message for the last two days, but this morning, had one appointment open up in January. I snagged it, and the next time I went in to schedule it gave me the "Currently there are no available appointments at this enrollment center. Please check later for openings or choose another enrollment center" message. So just keep checking in.