File Menu ArcGIS Online objects within ArcMap do not respect proxy values. Any organization with traffic forced through a proxy will not be able to use the "Sign In...", "Add Data", or "ArcGIS Online..." objects. Affected clients may crash or hang when performing any operations associated with the File menu.
1. Apply ArcGIS Desktop 10.0 SP12. Open <a href="http://www.arcgis.com/home/group.html?owner=esri&title=ArcGIS%20Online%20Basemaps" target="_blank">http://www.arcgis.com/home/group.html?owner=esri&title=ArcGIS%20Online%20Basemaps</a>3. Identify the desired basemap; Select Open > Open in ArcGIS Desktop 10.(See attached powerpoint presentation)