I left out a word You need to be sure you have a valid *default* basemap configured. That means, outside of just the basemap gallery, that you have specified what the default basemap is for your organization. I've checked, and the steps Scott left should get you to the right spot: in "My Organization" click "Edit Settings", choose the "Map" tab, and make sure a basemap (that opens successfully) is set in the "Default Basemap" section.
If it does have one there, please let us know and we can look into this further.
Thanks!
Esri Education Team