This tool requires a minimum of 30 features after aggregation. For incident data when you provided Polygons For Aggregating Incidents Into Counts, the aggregation process involves counting the number of features in each polygon, then analyzing the polygons with their associated counts. You provided a feature class with fewer than 30 aggregation polygons.
This tool will work with a selection set. If your Polygons For Aggregating Incidents Into Counts feature layer has at least 30 valid polygon features, check to see if there is an active selection set limiting the number of polygons used in the analysis; otherwise, you can provide a different feature layer for the Polygons For Aggregating Incidents Into Counts or use a different Incident Aggregation Method. Another option is to select an attribute in the Input Features to serve as an Analysis Field in which case aggregation becomes unnecessary.