Hi all,
I also encounter this illegal string offset error in a multilingual OJS3 install which was migrated from OJS2 and previously used a lot the import/export plugin.
I looked thorugh the user_settings and author_settings tables as suggested in the other thread and there seemed to be no problems.
However, in the submission_file_settings table there are some rows which have blanks in the locale field and the setting_name is old-supp-id for all these rows. May this cause the error?
Thanks.