This tool includes an optional output parameter that uses the Spatial Analyst extension. This extension must be enabled in the application in which you are using it. The Density Surface will be clipped to the raster analysis mask specified in the environment settings. If no raster mask is specified, you will need an Desktop Advanced license, as the output raster layer will be clipped to a convex hull around the Input Features.
From within the application, click Licensing from the Catalog pane. Verify that Spatial Analyst is in the list of Installed Extensions. If Spatial Analyst is available in the list of extensions, but is unavailable, the license has not been activated. If Spatial Analyst does not appear in the list of extensions, it must be installed. See the administrator of your organization for more information.