The dynamic workspace referenced by this map service has not been registered with the server. Registering a dynamic workspace with the server helps ensure that the server has access to all the data from that workspace.
When you publish a map service to ArcGIS Server, you can optionally choose to allow clients of ArcGIS Server, such as the ArcGIS Web APIs, to add a layer from one of the registered workspaces in your map service programmatically per request. Map service dynamic layers offer you a way to enhance client applications by providing your users with a rich experience on the web.
For a full list of the functionality exposed by dynamic layers in a map service, see the topic Supported functionality in map services.