about cpm material

I write codes like this:
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from yade import pack,geom,qt
from yade.gridpfacet import *
from pylab import *

O.engines=[
ForceResetter(),
InsertionSortCollider([
Bo1_Sphere_Aabb(),Bo1_GridConnection_Aabb(),Bo1_Facet_Aabb(),
]),
InteractionLoop(
[Ig2_Sphere_Sphere_ScGeom(),
Ig2_Facet_Sphere_ScGeom(),
Ig2_Sphere_GridConnection_ScGridCoGeom(),
Ig2_GridNode_GridNode_GridNodeGeom6D(),
Ig2_GridConnection_GridConnection_GridCoGridCoGeom(),],
[Ip2_CpmMat_CpmMat_CpmPhys(),
Ip2_FrictMat_CpmMat_FrictPhys(),
Ip2_CohFrictMat_CohFrictMat_CohFrictPhys(setCohesionNow=True,setCohesionOnNewContacts=False)],
[Law2_ScGeom_CpmPhys_Cpm(),
Law2_ScGeom_FrictPhys_CundallStrack(),
Law2_ScGeom6D_CohFrictPhys_CohesionMoment(),
Law2_ScGridCoGeom_FrictPhys_CundallStrack()]
),
NewtonIntegrator(gravity=(0,0,-10),damping=0.1,label='newton')]

O.materials.append(CohFrictMat(young=3e2,poisson=0.3,density=1e1,frictionAngle=10,normalCohesion=1e7,shearCohesion=1e7,momentRotationLaw=True,label='spheremat'))

O.materials.append(FrictMat(young=3e2,poisson=.25,frictionAngle=0.5,density=1e1,label='face'))

O.materials.append(CpmMat(density=1e1,young=3e2,poisson=0.25,frictionAngle=0.5,sigmaT=2e1,epsCrackOnset=1e-4,relDuctility=30,label='spheresh'))
### Parameters of a rectangular grid ###
L=0.1 #length [m]
l=0.05 #width [m]
nbL=10 #number of nodes for the length [#]
nbl=5 #number of nodes for the width [#]
r=L/100.0 #radius
color=[255./255.,102./255.,0./255.]
nodesIds=[]
#Create all nodes first :
for i in range(0,nbL):
for j in range(0,nbl):
nodesIds.append( O.bodies.append(gridNode([i*L/nbL,j*l/nbl,0],r,wire=False,fixed=False,material='spheremat',color=color)) )

#Create connection between the nodes
for i in range(0,len(nodesIds)):
for j in range(i+1,len(nodesIds)):
dist=(O.bodies[i].state.pos - O.bodies[j].state.pos).norm()
if(dist<=L/nbL*1.01):
O.bodies.append( gridConnection(i,j,r,color=color) )

#Set a fixed node
O.bodies[0].dynamic=False
O.bodies[4].dynamic=False
O.bodies[45].dynamic=False
O.bodies[49].dynamic=False

O.bodies.append(sphere([0.05,0.025,0.01],0.0061,material='spheresh'))
O.bodies.append(sphere([0.04,0.023,0.01],0.0021,material='spheresh'))
O.bodies.append(sphere([0.03,0.028,0.008],0.0061,material='spheresh'))
S1=len(O.bodies)

O.bodies.append(geom.facetBox((L/2.0,l/2.0,-0.01),(L*1.2/2,l*1.2/2,L),wallMask=63,material='face'))

S2=len(O.bodies)

for i in range(S1,S2):
O.bodies[i].dynamic=False

O.dt=1e-06

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After some timr it runs, I get the message:
--------------------------------------------------------------------------
FATAL /home/dj/yade/trunk/pkg/dem/ConcretePM.cpp:380 go: Verification `!std::isnan(epsN)' failed!
FATAL /home/dj/yade/trunk/pkg/dem/ConcretePM.cpp:380 go: in interaction #137+#83
terminate called without an active exception
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can you tell me what's wrong with it?Thanks a lot!