I had the same thing happen on one of my sites, but the other way around. First it wasn't working, then after a few days it worked again. Since then I haven't seen any problems with it. I hadn't done anything to fix it (although I tried). I looked around the internet and read through the Google docs on the subject, but the only "help" I found was that you need to make sure that your profiles are not being blocked. Which profile wasn't clear, whether it be the user's profile or the site's profile, but I checked both (and they weren't blocked, as far as I could tell). I wasn't all that surprised, though, as they are still working out the kinks.
If no one else comes up with a solution, just give it a couple of days before you tackle the problem again. I'll keep an eye on this question, because I'd like to hear in the end how your problem works out.