dotnet/machinelearning · error · NotSupportedException

Unsupported task type

Error message

Unsupported task type: {task}

What it means

GetAllowedLabelTypes maps an AutoML TaskKind to the label DataViewTypes that task supports. If the task falls through the switch, NotSupportedException 'Unsupported task type' is thrown — meaning the task value isn't one of binary/multiclass/regression/recommendation/ranking.

Solutions

1. Use a supported task: binary/multiclass classification, regression, recommendation, or ranking.
2. Update the Microsoft.ML.AutoML package to a version matching the task enum value you specify.
3. Log the actual task value to confirm what is being passed; fix the config/code mapping.

Example fix

// before
var settings = new MulticlassExperimentSettings(...); // task resolved to unknown kind on older package
// after
dotnet add package Microsoft.ML.AutoML --version <latest>
var experiment = mlContext.Auto().CreateMulticlassExperiment(settings);

var supported = new[] { "binary-classification", "multiclass-classification", "regression", "recommendation", "ranking" };
if (!supported.Contains(taskName)) throw new InvalidOperationException($"task {taskName} not supported by this ML.NET version");

bool IsKnownTaskKind(TaskKind kind) =>
    kind is TaskKind.BinaryClassification or TaskKind.MulticlassClassification or TaskKind.Regression or TaskKind.Recommendation or TaskKind.Ranking;

try { result = experiment.Execute(trainData, settings); }
catch (NotSupportedException ex) when (ex.Message.StartsWith("Unsupported task type")) { /* fall back to a supported task or upgrade package */ }

When it happens

Trigger: Passing a TaskName/Task to AutoML APIs whose mapped TaskKind isn't handled (future/unknown enum value, default case), typically via ValidateColumnInformation during Execute on a newer enum value used with an older ML.NET build.

Common situations: Assembly/version mismatch where a new task enum was serialized or specified but the loaded Microsoft.ML.AutoML doesn't recognize it; typo casting an int to TaskKind; configuration-driven task names mapped incorrectly.

Related errors

• column must be of data type
• Duplicate column name
• File at path ' ' cannot be empty
• File ' ' does not exist
• If provided, must be the same as for Ranking Experiments

AI-assisted analysis of dotnet/machinelearning@7b76e69cf9 (2026-09-11). Data as JSON: /api/errors/5f53e3e97a0ccba1. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.ML.AutoML/Utils/UserInputValidationUtil.cs:323

        }

        private static IEnumerable<DataViewType> GetAllowedLabelTypes(TaskKind task)
        {
            switch (task)
            {
                case TaskKind.BinaryClassification:
                    return new DataViewType[] { BooleanDataViewType.Instance };
                // Multiclass label types are flexible, as we convert the label to a key type
                // (if input label is not already a key) before invoking the trainer.
                case TaskKind.MulticlassClassification:
                    return null;
                case TaskKind.Regression:
                case TaskKind.Recommendation:
                    return new DataViewType[] { NumberDataViewType.Single };
                case TaskKind.Ranking:
                    return new DataViewType[] { NumberDataViewType.Single };
                default:
                    throw new NotSupportedException($"Unsupported task type: {task}");
            }
        }
    }
}

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