오류: 이미 존재하는 엔티티를 추가할 수 없습니다.

 public bool ImportToPool()
        {
            DataTable dt = ImportExcel();
            //return DAL.SmsPoolService.ImportFromDataBable(dt);
            ////SmsPool Pool = new SmsPool();

            ////Pool.ApplyID = this.ApplyID;
            ////Pool.NetOperationID = 0;
            ////Pool.PriorityLevel = 0;

            ////Pool.CheckFlag = " ";
            ////Pool.CheckContentFlag = " ";

            string[] numArr = this.Numbers.Trim(',').Split(',');
            //Pool.SrcNumbers = this.Numbers;
            //Pool.ObjNum = "";
            //Pool.SmsContent = "";
            //Pool.SmsCount = 0;            
            DAL.SmsPoolService PoolSvs = new SmsPoolService();
            ////SmsPool Pool = new SmsPool();// 
            for (int i = 0; i < dt.Rows.Count; i++)
            {
                //DAL.SmsPoolService PoolSvs = new SmsPoolService();
                SmsPool Pool = new SmsPool();

                Pool.ApplyID = this.ApplyID;
                Pool.NetOperationID = 0;
                Pool.PriorityLevel = 0;

                Pool.CheckFlag = " ";
                Pool.CheckContentFlag = " ";

                Pool.SrcNum = numArr[i%numArr.Length];
                Pool.ObjNum = dt.Rows[i][0].ToString();
                Pool.SmsContent = dt.Rows[i][1].ToString();
                Pool.SmsCount =(int) Math.Ceiling((Pool.SmsContent.Length * 0.1) / MyConst.SmsMaxCharCount);
                PoolSvs.Insert(Pool);
            }
            return true;
        }