using System;

public class Program

{

    public static void Main()

    {

        String errorString= "System.IO.DirectoryNotFoundException:.Could.not.find.a.part.of.the.path.'c:/upload/Training/data.csv'......at.System.IO.__Error.WinIOError(Int32.errorCode,.String.maybeFullPath).....at.System.IO.FileStream.Init(String.path,.FileMode.mode,.FileAccess.access,.Int32.rights,.Boolean.useRights,.FileShare.share,.Int32.bufferSize,.FileOptions.options,.SECURITY_ATTRIBUTES.secAttrs,.String.msgPath,.Boolean.bFromProxy,.Boolean.useLongPath,.Boolean.checkHost).....at.System.IO.FileStream..ctor(String.path,.FileMode.mode,.FileAccess.access,.FileShare.share,.Int32.bufferSize,.FileOptions.options,.String.msgPath,.Boolean.bFromProxy).....at.System.IO.FileStream..ctor(String.path,.FileMode.mode,.FileAccess.access,.FileShare.share,.Int32.bufferSize,.Boolean.useAsync).....at.Frends.File.File.<ExecuteRead>d__12.MoveNext()..---.End.of.stack.trace.from.previous.location.where.exception.was.thrown.---.....at.System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw().....at.System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task.task).....at.Frends.File.File.<ExecuteActionAsync>d__9 1.MoveNext()..---.End.of.stack.trace.from.previous.location.where.exception.was.thrown.---.....at.System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw().....at.System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task.task).....at.Frends.File.File.<Read>d__0.MoveNext()..---.End.of.stack.trace.from.previous.location.where.exception.was.thrown.---.....at.System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw().....at.System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task.task).....at.System.Runtime.CompilerServices.ConfiguredTaskAwaitable 1.ConfiguredTaskAwaiter.GetResult().....at.Frends.ExecutableProcess.frends_Test.frends_Test.<ExecuteAsync>d__0.MoveNext().in.Frends.ExecutableProcess.frends_Test.cs:line.57";

        int enderror = errorString.IndexOf("....");

        Console.WriteLine(enderror);

        String message = errorString.Substring(0,enderror);

        Console.WriteLine(message+ " - see more details in FRENDS");

    }

}

​