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    public class InvaildSessionException : System.Exception

    {

        public InvaildSessionException() : base() {}

        public InvaildSessionException(string message) : base(message) { }

        public InvaildSessionException(string message, System.Exception inner) : base(message, inner) { }

        // A constructor is needed for serialization when an

        // exception propagates from a remoting server to the client. 

        protected InvaildSessionException(System.Runtime.Serialization.SerializationInfo info,

            System.Runtime.Serialization.StreamingContext context)

        { }

    }

https://msdn.microsoft.com/ko-kr/library/ms173163.aspx