PicklingError

Sorry to bother you sir,

My YADE version is yade-2019.01a and I am working on Ubuntu 18.04. I am trying to run biaxialSmooth.py from FEM-DEM examples.
Then get the error I get is this:

PicklingError: Can't pickle <type 'function'>: attribute lookup __builtin__.function failed.

I have read the same issue in https://answers.launchpad.net/yade/+question/686704 , and his solution is

 '' It is all about paths. Where and how you creat yadeimport.py, where you export your python path''

but i am still confused how to change and export the python path. Here is a detailed explanation of what I did. I followed the instruction in the biaxialSmooth.py by

1- sudo apt install python-escript

2- cd examples/FEMxDEM

3-export PYTHONPATH="/usr/lib/python-escript:/home/weicc/下载/dem-fem-couplinp master/installation/_build/yade/source/examples/FEMxDEM"

4-export LD_LIBRARY_PATH='/usr/lib/python-escript/lib'

5-ln -s '/home/weicc/下载/dem-fem-coupling-master/installation/_build/yade/source/examples/FEMxDEM/yadeimport.py'

and it show the worning:'' ln: Could not create symbolic link './yadeimport.py': File already exists

Here is the output:

Welcome to Yade 2019.01a
TCP python prompt on localhost:9000, auth cookie `cyueks'
XMLRPC info provider on http://localhost:21000
Running script biaxialSmooth.py
=======================================================================
For better performance compile python-escript with direct solver method
=======================================================================
Press Enter to continue...
Traceback (most recent call last):
  File "/home/weicc/下载/dem-fem-coupling-master/installation/_build/yade/install/bin/yade", line 241, in runScript
    execfile(script,globals())
  File "biaxialSmooth.py", line 43, in <module>
    prob = MultiScale(domain=mydomain,ng=numg,np=nump,random=False,rtol=1e-2,usePert=False,pert=-2.e-5,verbose=True)
  File "/home/weicc/下载/dem-fem-coupling-master/installation/_build/yade/source/examples/FEMxDEM/msFEM2D.py", line 85, in __init__
    self.__scenes=self.__pool.map(initLoad,range(ng))
  File "/usr/lib/python2.7/multiprocessing/pool.py", line 253, in map
    return self.map_async(func, iterable, chunksize).get()
  File "/usr/lib/python2.7/multiprocessing/pool.py", line 572, in get
    raise self._value
PicklingError: Can't pickle <type 'function'>: attribute lookup __builtin__.function failed

Looking forward to a piece of advice!