using System;

using System.Linq;

using System.Threading.Tasks;

​

public class Program

{

    public static async Task Main()

    {

        var source = Enumerable.Range(1, 10);

        var options = new ParallelOptions() { MaxDegreeOfParallelism = 5 };

        var task = Parallel.ForEachAsync(source, options, async (item, token) =>

        {

            await Task.Delay(100, token);

            if (item == 5) throw new ApplicationException("Oops!");

            await Task.Delay(100, token);

        });

        try

        {

            await task;

        }

        catch when (task.IsFaulted)

        {

            foreach (var error in task.Exception.InnerExceptions)

                Console.WriteLine($"{error.GetType().Name}: {error.Message}");

        }

    }

}