I haven't had this happen, so I don't know the cure, fer sure.
But give these things a try
- Have a peek in the settings to verify that your nook is finding [bold]your[/bold] wifi & not someone elses
- In settings, also verify that you email address is correct, and that it's the same on used in your account on the B&N site.
- If all else fails, turns your Nook off for a few seconds, and power it on again. RE-Boot sorts out a lot of things.