Undefined offset: 33 (theme_room_reservations() in room_reservations_calendar.view.inc)

Hello,

I recently install room_reservation for study purpose, but after adding a few "Room Reservations Category" i got this error:

    Notice: Undefined variable: selected_category in theme_room_reservations() (line 137 of /partages/priv/btsdcg/info1/e.desbrosses/public_html/PPE13/drupal/modules/room_reservations/view/room_reservations_calendar.view.inc).
    Notice: Undefined offset: 33 in theme_room_reservations() (line 317 of /partages/priv/btsdcg/info1/e.desbrosses/public_html/PPE13/drupal/modules/room_reservations/view/room_reservations_calendar.view.inc).
    Notice: Undefined variable: selected_category in theme_room_reservations() (line 137 of /partages/priv/btsdcg/info1/e.desbrosses/public_html/PPE13/drupal/modules/room_reservations/view/room_reservations_calendar.view.inc).
    Notice: Undefined offset: 33 in theme_room_reservations() (line 317 of /partages/priv/btsdcg/info1/e.desbrosses/public_html/PPE13/drupal/modules/room_reservations/view/room_reservations_calendar.view.inc).
    Notice: Undefined variable: selected_category in theme_room_reservations() (line 137 of /partages/priv/btsdcg/info1/e.desbrosses/public_html/PPE13/drupal/modules/room_reservations/view/room_reservations_calendar.view.inc).
    Notice: Undefined offset: 33 in theme_room_reservations() (line 317 of /partages/priv/btsdcg/info1/e.desbrosses/public_html/PPE13/drupal/modules/room_reservations/view/room_reservations_calendar.view.inc).

I was able to correct the "Undefined variable" errors with the patch from this subject

unfortunately, I didn't found anything for the "Undefined offset: 33". It seems this offset error change from "33" to "52" when I try to change the day using the calendar.

Do you know what is happening and how (if possible) can i fix it ?