Python : Strange multiprocessing function crash in console - python-2.7

Question

I maintain an experimental tool that still python 2.7 that use a bunch of libraries, such as Gdal, shapely, astropy, OpenCV2, scipy, etc. Everything was fine until the system as changed, so virtual environment has been redone and then I have a problem with multiprocessing function.
The most simplified code to reproduce the behaviour:
import multiprocessing
if __name__ == '__main__':
cpus = multiprocessing.cpu_count()
cpus = cpus - 1
pool = multiprocessing.Pool(processes=cpus)
Result #1 with:
Python : VirEnv 2.7 build
Console : Pycharm PyDev console
Traceback (most recent call last): File "", line 1, in
Traceback (most recent call last): File "", line 1,
in File "C:\Python27\Lib\multiprocessing\forking.py", line
380, in main
prepare(preparation_data) File "C:\Python27\Lib\multiprocessing\forking.py", line 504, in prepare
File "C:\Python27\Lib\multiprocessing\forking.py", line 380, in main
file, path_name, etc = imp.find_module(main_name, dirs) ImportError: No module named input
prepare(preparation_data) File "C:\Python27\Lib\multiprocessing\forking.py", line 504, in prepare
file, path_name, etc = imp.find_module(main_name, dirs) ImportError: No module named input
Why it is looking into "C:\Python27\Lib\multiprocessing\" instead of the VirEnv 2.7 build?
Result #2 with:
Python : VirEnv 2.7 from Anaconda
Console : Pycharm PyDev console
Traceback (most recent call last): File "", line 1, in
File
"C:\Users\_____\AppData\Local\conda\conda\envs\Python_27\lib\multiprocessing\spawn.py",
line 105, in spawn_main
exitcode = _main(fd) File "C:\Users\_____\AppData\Local\conda\conda\envs\Python_27\lib\multiprocessing\spawn.py",
line 114, in _main
prepare(preparation_data) File "C:\Users\_____\AppData\Local\conda\conda\envs\Python_27\lib\multiprocessing\spawn.py",
line 225, in prepare
_fixup_main_from_path(data['init_main_from_path']) File "C:\Users\_____\AppData\Local\conda\conda\envs\Python_27\lib\multiprocessing\spawn.py",
line 277, in _fixup_main_from_path
run_name="mp_main") File "C:\Users\_____\AppData\Local\conda\conda\envs\Python_27\lib\runpy.py",
line 261, in run_path
code, fname = _get_code_from_file(run_name, path_name) File "C:\Users\_____\AppData\Local\conda\conda\envs\Python_27\lib\runpy.py",
line 231, in _get_code_from_file
with open(fname, "rb") as f: OSError: [Errno 22] Invalid argument: 'B:\WorkingSpace\_____\API\'
Result #3 with:
Python : VirEnv 2.7 build
Console : Pycharm terminal
Passed without error
Result #4 with:
Python : VirEnv 2.7 from Anaconda
Console : Pycharm terminal
Passed without error
Result #5 with:
Python : VirEnv 2.7 from Anaconda
Console : Anaconda terminal
Passed without error
So, Pycharm PyDev console seems where only the crash occurs? Why? How to get rid of this?
In addition :
After the console initialization, I have:
B:\WorkingSpace\_____\API\virEnv_Desktop_V2.7\Scripts\python.exe "C:\Program Files\JetBrains\PyCharm Community Edition 2019.2\helpers\pydev\pydevconsole.py" --mode=client --port=_____
import sys; print('Python %s on %s' % (sys.version, sys.platform))
sys.path.extend(['B:\\WorkingSpace\\_____\\API', 'B:/WorkingSpace/_____/API'])
PyDev console: starting.
Python 2.7.16 (v2.7.16:413a49145e, Mar 4 2019, 01:37:19) [MSC v.1500 64 bit (AMD64)] on win32
When I pass the simplified code to reproduce the behaviour, the error "ImportError: No module named " occur in the forking.py which is in the path "C:\Python27\Lib\multiprocessing\".
Sys.path are:
'C:\Program Files\JetBrains\PyCharm Community Edition
2019.2\helpers\pydev',
'C:\Program Files\JetBrains\PyCharm Community Edition 2019.2\helpers\third_party\thriftpy',
'C:\Program Files\JetBrains\PyCharm Community Edition 2019.2\helpers\pydev',
'C:\Windows\SYSTEM32\python27.zip',
'B:\WorkingSpace\_____\API\virEnv_Desktop_V2.7\DLLs',
'B:\WorkingSpace\_____\API\virEnv_Desktop_V2.7\lib',
'B:\WorkingSpace\_____\API\virEnv_Desktop_V2.7\lib\plat-win',
'B:\WorkingSpace\_____\API\virEnv_Desktop_V2.7\lib\lib-tk',
'B:\WorkingSpace\_____\API\virEnv_Desktop_V2.7\Scripts',
'C:\Python27\Lib',
'C:\Python27\DLLs',
'C:\Python27\Lib\lib-tk',
'B:\WorkingSpace\_____\API\virEnv_Desktop_V2.7',
'B:\WorkingSpace\_____\API\virEnv_Desktop_V2.7\lib\site-packages',
'B:\WorkingSpace\_____\API',
'B:/WorkingSpace/_____/API'
What happening?