You won't be able to use the online portion of Super Mario Maker for a good few hours.
Nintendo has announced that an extended maintenance is taking place on the network, affecting Super Mario Maker's online play. The downtime time started about an hour ago and will go on for a good few hours more.
37.5 hours, to be precise. According to Nintendo it started at 3:30am PST (11:30am UK) on January 27, and won't come back online until 5pm PST (1am UK Jan 29) on January 28.
You can play the game itself but you can't browse, upload or download courses.