When opening a Web map in ArcGIS Desktop ArcMap version 10, the following error message is displayed:
"Invalid Web Map. Web Map must have at least one layer present."
At version 10 service pack 1, the following error message is displayed:
"Could not open the specified file"
This is a known issue caused by an update released for ArcGIS.com, which occurs with new Web maps created after March 2, 2011, or existing Web maps that have been modified and saved after that date.
Web maps with a last modified date of March 2, 2011 or earlier can still be opened in ArcGIS Desktop 10. This applies to Web maps created in ArcGIS.com and the ArcGIS Explorer Online client.
10.0 Service Pack 3 is intended to allow Web maps in the new format to be opened in ArcMap 10.0, but not all of the data types that can be found in ArcGIS Web maps are supported in 10.0 SP3. For example, layers containing note features and annotations drawn on top of the map are not supported.