When trying to anonymously open an operation view in a web browser, which references an ArcGIS Online web map containING an ArcGIS for Server cached map service basemap with a custom tiling scheme, the following error is returned,"An unknown error occurred."
1) Use an ArcGIS Online basemap service.
2) Create a custom cached map service with ArcGIS for Server using the default ArcGIS Online/Bing Maps/Google Maps tiling scheme.