I have created a group (call it "Basemaps") in my organisation account in ArcGIS Online and published a number of maps with a single layer defined as a basemap. All of these maps are shared both with the organisation and the Basemaps group.
I have then added a number of users to the Basemap group.
I have also edited the Organisation settings in ArcGIS online to use the basemap gallery from the "Basemaps" group rather than the standard ESRI basemaps.
When I go to create a new map and click on the basemaps gallery, I see a drop-down with all the basemaps I have created. If I click on these I am able to use them.
When any other user who has been added to the "Basemaps" group does the same, they see the basemaps I have created, but when they click on it they get an error telling them that the basemap is unavailable.
Any ideas what I might have missed?