I have a similar error trying to migrate from Plesk 12.5 to Plesk 17.8.
Exception:
Traceback (most recent call last):
File "/usr/local/psa/admin/plib/modules/panel-migrator/backend/lib/python/parallels/plesk/source/plesk/actions/content/web/copy_unix_content.py", line 108, in run...