HI,
I am relatively new in oTree. I designed a game with 4 players with 2 groups. However, while running in devserver to test, I am getting the following error after clicking on the link. Any help would be appreciated.

Thank you very much.

creating_session
Please wait, creating session.

Failed to create session: 'set' object is not subscriptable
Traceback (most recent call last):
  File "p:\personal\otree_codes\venv\lib\site-packages\otree\session.py", line 447, in create_session_traceback_wrapper
    return create_session(**kwargs)
  File "p:\personal\otree_codes\venv\lib\site-packages\otree\session.py", line 357, in create_session
    if ppg is None or Subsession._has_group_by_arrival_time():
  File "p:\personal\otree_codes\venv\lib\site-packages\otree\models\subsession.py", line 135, in _has_group_by_arrival_time
    return has_group_by_arrival_time(app_name)
  File "p:\personal\otree_codes\venv\lib\site-packages\otree\common.py", line 165, in has_group_by_arrival_time
    page_sequence[0], 'group_by_arrival_time', False
TypeError: 'set' object is not subscriptable