Error in upgrading from xubuntu to trisquel

When upgrading from Ubuntu to Trisquel using this shell script
https://trisquel.info/en/wiki/migrate-ubuntu-trisquel-without-reinstalling
I got the following errors:

Unpacking replacement python-greenlet ...
Processing triggers for man-db ...
Processing triggers for ufw ...
Processing triggers for ureadahead ...
ureadahead will be reprofiled on next reboot
Processing triggers for software-center ...
ERROR:root:DebFileApplication import
Traceback (most recent call last):
File "/usr/share/software-center/softwarecenter/db/__init__.py", line 4, in
from debfile import DebFileApplication, DebFileOpenError
File "/usr/share/software-center/softwarecenter/db/debfile.py", line 25, in
from softwarecenter.db.application import Application, AppDetails
File "/usr/share/software-center/softwarecenter/db/application.py", line 27, in
import softwarecenter.distro
File "/usr/share/software-center/softwarecenter/distro/__init__.py", line 194, in
distro_instance = _get_distro()
File "/usr/share/software-center/softwarecenter/distro/__init__.py", line 169, in _get_distro
module = __import__(distro_id, globals(), locals(), [], -1)
ImportError: No module named Trisquel
Traceback (most recent call last):
File "/usr/sbin/update-software-center", line 38, in
from softwarecenter.db.update import rebuild_database
File "/usr/share/software-center/softwarecenter/db/update.py", line 33, in
from softwarecenter.distro import get_distro
File "/usr/share/software-center/softwarecenter/distro/__init__.py", line 194, in
distro_instance = _get_distro()
File "/usr/share/software-center/softwarecenter/distro/__init__.py", line 169, in _get_distro
module = __import__(distro_id, globals(), locals(), [], -1)
ImportError: No module named Trisquel