I've had this a couple of times. I don't know whether its coincidence, but both have been on visits to the shop channel, both of which required the plug to be pulled on the console before they would synch again.
I've also had the console lock up completely a couple of times when trying to access the disc channel, again requiring the plug to be pulled.
I'm hoping that it will be sorted in the next firmware update, but I've not been too impressed with the operating system thus far. It does make me wonder if nintendo have rushed the console into production to facilitate a pre-christmas launch.