Problem with a coordinated task sequence. Could somebody please help spotting the problem?

Ladies and Gentlemen,

I am stuck trying to simulate a simple AGV-based order fulfillment line.
The tasks are generated by a "WMS" (A basic FR, used as a control center) and handled by two AGVs. The AGVs go through the pallet loading station, than order fullfillment area, unloading dock, and staging (parking) area.
Exclusive access is implemented by approaching the entry of a workcell, trying to allocate the operator of this workcell, and proceeding in only after the operator has been allocated.


I have ran into several problems and I worked around one, but cannot solve the other.

Problem 1:
When I use more than one TaskExecuter, my CTS fails straight away if the CALLSUBTASKS is the first proxy task. I worked around it by adding a proxytask DELAY at the beginning of the tasksequence, but I do not understand the reason for the problem or why the solution worked.
I am a bit worried about this.


Problem 2:
When I use more than one TaskExecuter, the last generated task always fails.
In the attached model, I generate 10 tasks in a loop (10 orders sent from the "WMS"). The last one fails.
I tried to change it to 100 and still the last one fails.
I commented out all materials handling operations, leaving only allocations, TRAVEL, and TRAVELTOLOC proxy tasks, to reduce the number of possible causes.
The problem seems fundamental in nature - I must be doing something wrong.

Here is the code for the task sequence in question:

/**Dispatch orders*/
treenode current = ownerobject(c);
int msgCode = msgparam(1);
/* Message is fired by the one-off user event */
if (msgCode == START_SIMULATION)
{
 for (int i = 1; i <= 10; i++)
 {
  treenode cts = createcoordinatedtasksequence(vehicleProxy);
  int agvKey = insertallocatetask(cts, vehicleProxy, PICKING_PRIO, PREEMPT_NOT);
  int dummy;
  /* When this task is not included, task sequence immediately fails on startup. Why??? */
  dummy = insertproxytask(cts, agvKey, TASKTYPE_DELAY, NULL, NULL, 0);
  insertsynctask(cts, dummy);
  int prepVehicle = insertproxytask(cts, agvKey, TASKTYPE_CALLSUBTASKS, current, NULL, PREPARE_VEHICLE);
  insertsynctask(cts, prepVehicle);
  int loadOrders = insertproxytask(cts, agvKey, TASKTYPE_CALLSUBTASKS, current, NULL, PERFORM_PICK);
  insertsynctask(cts, loadOrders);
  int unloadVehicle = insertproxytask(cts, agvKey, TASKTYPE_CALLSUBTASKS, current, NULL, UNLOAD_VEHICLE);
  insertsynctask(cts, unloadVehicle);
  int parkVehicle = insertproxytask(cts, agvKey, TASKTYPE_CALLSUBTASKS, current, NULL, PARK_VEHICLE);
  insertsynctask(cts, parkVehicle);  
  dummy = insertproxytask(cts, agvKey, TASKTYPE_DELAY, NULL, NULL, 0);
  insertsynctask(cts, dummy);
  insertdeallocatetask(cts, agvKey);
  profiletasksequence(cts);
  dispatchcoordinatedtasksequence(cts);
 }
}
/* Load a pallet on the AGV */
else
if (msgCode == PREPARE_VEHICLE)
{
 treenode palletDisplenserStation =  node("/PalletDispenserStation", model());
 treenode terminal =  node("/VehicleControlTerminal", model());
 treenode palletDispenser =  node("/PalletDispenser", model());
 treenode agv = msgsendingobject();
 treenode placeFunc = node("/MAIN:/project/model/Tools/UserCommands/PlaceItemInAShortPc/code", model());
 treenode cts = createcoordinatedtasksequence(agv);
 int agvKey = insertallocatetask(cts, agv, PICKING_PRIO,PREEMPT_NOT); 
 int opKey = insertallocatetask(cts, vehicleDispatcherProxy, PICKING_PRIO,PREEMPT_ONLY); 
 int gotoControl = insertproxytask(cts, opKey, TASKTYPE_TRAVELTOLOC, NULL, NULL, xloc(terminal), yloc(terminal), 0);
 insertsynctask(cts, gotoControl);
 int opStartVehicle = insertproxytask(cts, opKey, TASKTYPE_DELAY, NULL, NULL, 2);
 insertsynctask(cts, opStartVehicle);
 int appr2 = insertproxytask(cts, agvKey, TASKTYPE_TRAVEL, palletDisplenserStation);
 insertproxytask(cts, opKey, TASKTYPE_TRAVELTOLOC, NULL, NULL, xloc(palletDispenser), yloc(palletDispenser), 0);
 treenode item = NULL;
 /* Materials Handling operation has been commented out
 //v
 for (int i= 1; i <= content(palletDispenser); i++)
 {
  item = rank(palletDispenser, i);
  treenode tmp = label(item,"allocated");
  if (!objectexists(tmp))
  {
   assertlabel(item, "allocated", DATATYPE_NUMBER);
   break;
  }
 }
 insertproxytask(cts, opKey, TASKTYPE_FRLOAD, item, palletDispenser);
 */
 int appr1 = insertproxytask(cts, opKey, TASKTYPE_TRAVELTOLOC, NULL, NULL, xloc(palletDisplenserStation), yloc(palletDisplenserStation), 0);
 /* Materials Handling operation has been commented out 
 //v
 int dropPallet = insertproxytask(cts, opKey, TASKTYPE_FRUNLOAD, item, agv);
 insertsynctask(cts, dropPallet);
 insertproxytask(cts, opKey, TASKTYPE_NODEFUNCTION, placeFunc, NULL, tonum(item));
 */
 int opLoadPallet = insertproxytask(cts, opKey, TASKTYPE_DELAY, NULL, NULL, 0);
 insertproxytask(cts, opKey, TASKTYPE_TRAVELTOLOC, NULL, NULL, xloc(terminal), yloc(terminal), 0);
 insertdeallocatetask(cts, opKey);
 insertdeallocatetask(cts, agvKey);
 return cts;
}
else
/* Fulfill the order */
if (msgCode == PERFORM_PICK)
{
 treenode rack =  node("/Rack", model());
 treenode station =  node("/OrderPickerStation", model());
 treenode agv = msgsendingobject();
 treenode dest = first(agv);
 treenode cts = createcoordinatedtasksequence(agv);
 int agvKey = insertallocatetask(cts, agv, PICKING_PRIO,PREEMPT_NOT); 
 insertproxytask(cts, agvKey, TASKTYPE_TRAVEL, node("/PickAreaEntry", model()));
 int opKey = insertallocatetask(cts, orderPickerProxy, 0,0); 
 int approachRack = insertproxytask(cts, agvKey, TASKTYPE_TRAVEL, node("/PickArea", model()));
 insertsynctask(cts, approachRack);
 /* Materials Handling operation has been commented out
 //v
 treenode item = NULL;
 for (int i= 1; i <= content(rack); i++)
 {
  item = rank(rack, i);
  treenode tmp = label(item,"allocated");
  if (!objectexists(tmp))
  {
   break;
  }
 }
 for (int i = 1; i <= 8; i++)
 {
  assertlabel(item, "allocated", DATATYPE_NUMBER);
  insertproxytask(cts, opKey, TASKTYPE_FRLOAD, item, rack);
  insertproxytask(cts, opKey, TASKTYPE_UNLOAD, item, dest);
  item = next(item);
 }*/
 insertproxytask(cts, opKey, TASKTYPE_TRAVELTOLOC, NULL, NULL, xloc(station), yloc(station), 0);
 insertdeallocatetask(cts, opKey);
 insertdeallocatetask(cts, agvKey);
 return cts;
}
else
/* Unload the full pallet into the trailer */
if (msgCode == UNLOAD_VEHICLE)
{
 treenode unloadingDockEntry =  node("/UnloadingDockEntry", model());
 treenode unloadingDock =  node("/UnloadingDock", model());
 treenode gate =  node("/Gate", model());
 treenode station =  node("/TruckLoaderStation", model());
 treenode truck =  node("/Truck", model());
 treenode agv = msgsendingobject();
 treenode cts = createcoordinatedtasksequence(agv);
 int agvKey = insertallocatetask(cts, agv, PICKING_PRIO,PREEMPT_NOT); 
 insertproxytask(cts, agvKey, TASKTYPE_TRAVEL, unloadingDockEntry);
 int opKey = insertallocatetask(cts, truckLoaderProxy, PICKING_PRIO,PREEMPT_NOT); 
 insertproxytask(cts, agvKey, TASKTYPE_TRAVEL, unloadingDock);
 int gotoVehicle = insertproxytask(cts, opKey, TASKTYPE_TRAVELTOLOC, NULL, NULL, xloc(unloadingDock), yloc(unloadingDock), 0);
 insertsynctask(cts, gotoVehicle);
 int opStartVehicle = insertproxytask(cts, opKey, TASKTYPE_DELAY, NULL, NULL, 2);
 insertsynctask(cts, opStartVehicle);
 insertproxytask(cts, agvKey, TASKTYPE_TRAVEL, gate);
 /* Materials Handling operation has been commented out
 //v
 insertproxytask(cts, agvKey, TASKTYPE_FRUNLOAD, first(agv), truck);
 */
 int gotoStation = insertproxytask(cts, opKey, TASKTYPE_TRAVELTOLOC, NULL, NULL, xloc(station), yloc(station), 0);
 insertsynctask(cts, gotoStation);
 insertproxytask(cts, agvKey, TASKTYPE_TRAVEL, gate);
 insertdeallocatetask(cts, opKey);
 insertdeallocatetask(cts, agvKey);
 return cts;
}
else
/* Go to the vehicle staging area */
if (msgCode == PARK_VEHICLE)
{
 treenode agv = msgsendingobject();
 treenode parking = node(concat(nodetomodelpath(agv, true), "Parking"), model());
 treenode ts = createemptytasksequence(agv, PICKING_PRIO,PREEMPT_NOT); 
 inserttask(ts, TASKTYPE_TRAVEL, parking);
 return ts;
}
else
{
 msg("WMS Error", concat("Unhandled message: ", numtostring(msgCode), "\n from object: ", nodetomodelpath(msgsendingobject(), true)), 1);
 stop();
}

Please help!
Thank you!
Vadim

Ladies and Gentlemen,
I am happy to inform you that the problem has been identified.
As it turned out, the problem was not in the code of the CTS.
For a multi-vehicle configuration I was using one of the taskexecuters as a dispatcher to the other. That was a bad idea.
My CTS was structured in such a way that the top level task allocated taskexecuters from a pool and then called a series of subtasks (load, process, unload) which all had to be handled by the same TE. However, when the allocated TE was a team leader, on occasion that resulted in the subordinate TE being allocated for the subtask, which was resulting in chaos.
Replacing the master-slave relationship of the two TEs with a single dispatcher with links to both, has solved the problem.