pp.getForce() NRotSphere() terminates the simulation

Dear All,

When I use getForec for the NRotSphere I have the following problem.

gle$ mpirun.mpich -np 2 esysparticle bingle.py
0 -4.999 4.999 -4.999
===================================================================================
= BAD TERMINATION OF ONE OF YOUR APPLICATION PROCESSES
= PID 6915 RUNNING AT bwjliu-HP-ZBook-15
= EXIT CODE: 139
= CLEANING UP REMAINING PROCESSES
= YOU CAN IGNORE THE BELOW CLEANUP MESSAGES
===================================================================================
YOUR APPLICATION TERMINATED WITH THE EXIT STRING: Segmentation fault (signal 11)
This typically refers to a problem with your application.
Please see the FAQ page for debugging suggestion

The following is the simple bingle.py code where close to the end of the simulation I have added a while loop.
#bingle.py: A simple two-particle collision simulation using
# ESyS-Particle
# Author: D. Weatherley
# Date: 15 May 2007
# Organisation: ESSCC, University of Queensland
# (C) All rights reserved, 2007.
#
#
#import the appropriate ESyS-Particle modules:
from esys.lsm import *
from esys.lsm.util import Vec3, BoundingBox

#instantiate a simulation object
#and initialise the neighbour search algorithm:
sim = LsmMpi(numWorkerProcesses=1, mpiDimList=[1,1,1])
sim.initNeighbourSearch(
   particleType="NRotSphere",
   gridSpacing=2.5,
   verletDist=0.5
)

#specify the number of timesteps and timestep increment:
sim.setNumTimeSteps(10000)
sim.setTimeStepSize(0.001)
#specify the spatial domain for the simulation:
domain = BoundingBox(Vec3(-20,-20,-20), Vec3(20,20,20))
sim.setSpatialDomain(domain)

#add the first particle to the domain:
particle=NRotSphere(id=0, posn=Vec3(-5,5,-5), radius=1.0, mass=1.0)
particle.setLinearVelocity(Vec3(1.0,-1.0,1.0))
sim.createParticle(particle)

#add the second particle to the domain:
particle=NRotSphere(id=1, posn=Vec3(5,5,5), radius=1.5, mass=2.0)
particle.setLinearVelocity(Vec3(-1.0,-1.0,-1.0))
sim.createParticle(particle)

#specify the type of interactions between colliding particles:
sim.createInteractionGroup(
   NRotElasticPrms(
      name = "elastic_repulsion",
      normalK = 10000.0,
      scaling = True
   )
)

#Execute the simulation:
i = 0
while (i <=10):
 sim.runTimeStep()
 ParticleList = sim.getParticleList()
 for pp in ParticleList:
  print pp.getId(),pp.getPosition(),pp.getForce()
 i += 1
sim.exit()