Some of the records in the dataset have invalid geometry or invalid attribute data (or both). These records will not be included in the analysis.
Look for NULL values associated with any fields used in this analysis and replace the NULL values with non-NULL values, if possible. Also consider running the Repair Geometry tool on the input dataset to determine whether any of the geometry is invalid. When an output dataset is created by a tool giving this warning, it will be a subset of the input dataset (it will not contain the problem records); you can compare the input dataset to this output dataset to determine which records exhibit problems.