DI API: Picking list with different sales orders, error when pick up at different times.

Hello experts, I need your valuable assistance.

The issue is this, I have a pick list with different sales orders and by di api at different times I make the picking for each sales order. I have no problems with the first pick, but when I try to do it at another time throws me the following error:

1470000344 - Batch "NACIONAL" of item "DTC-C73-PVC3-0001" in bin location "QRO-GEN-ZR1" falls into negative inventory

My function (SAP BO 9.1 PL11):

int lRetCode = -1;

SAPbobsCOM.PickLists oPick = vCmp.GetBusinessObject(SAPbobsCOM.BoObjectTypes.oPickLists);

int sPL = 1502;

try

{

if (oPick.GetByKey(sPL))

       {

          oPick.Lines.SetCurrentLine(0);

          oPick.Lines.PickedQuantity = 1;

                  //oPick.Lines.OrderEntry = 16436;

                  //oPick.Lines.OrderRowID = 4;

          oPick.Lines.BatchNumbers.BatchNumber = "NACIONAL";

          oPick.Lines.BatchNumbers.Quantity = 1;

          oPick.Lines.BatchNumbers.Add();

          oPick.Lines.BinAllocations.BinAbsEntry = 149;

          oPick.Lines.BinAllocations.Quantity = 1;

          oPick.Lines.BinAllocations.SerialAndBatchNumbersBaseLine = 0;

          oPick.Lines.BinAllocations.BaseLineNumber = 0;

          oPick.Lines.BinAllocations.Add();

          lRetCode = oPick.Update();

                  if (lRetCode != 0)

          {

                      string sErr = string.Empty;

             vCmp.GetLastError(out lRetCode, out sErr);

                      return sErr;

                      // Console.WriteLine(sErr);

   }

                return"OK";

       }

            else

               return"No se encuentra documento";

}

catch (Exception ex)

{

      return ex.Message;

}

The problem is when I do the picking in different time for another sales order picking the same picking list.

In advance thanks and regards.