Have you updated your 3DS to the latest version of firmware?
If he wasn't up to date on his firmware, the system would ask him to update as soon as he tried to access the e-Shop.
Maybe your connection is at fault. Check if you can still access the internet via browser - or, if you have a game with online support, see if it can connect. --- "Evil, beware. We have waffles..." - Raven, Teen Titans