No basemap in the ArcGIS Location field

[DonBarker]

The similar post here
http://forums.arcgis.com/threads/37050-No-Map-when-viewing-list-item?highlight=location+field
got 400+ views but no reply from Esri.  Hope someone can reply this time.

Here is the same problem:

The ArcGIS Location field in the web part shows a blank background where a basemap should appear under a point.  See the image below.

I edited the config file LocationOnMapStartupMapDocument.xaml to change the ref from Topo to World Streets, then to Gray Canvas.  None of these worked.

(BTW, Esri, the documentation on this is not clear.  The Help page refs this file and MapWebPartStartupMapDocument for a variety of config changes.  But does not specify which file is for which changes.)

Any help appreciated.

Thanks.