Error validating the formula for column attendance

Question

hi

  When i write the below code in Formula i get above error

CASE
    WHEN (
        SELECT COUNT(*)
        FROM [SessionDeliveryParticipant] AS sub
        WHERE sub.SessionDeliveryCalendarID = [SessionDeliveryParticipant].SessionDeliveryCalendarID
        AND sub.PresentInSession = 0
    ) = (
        SELECT COUNT(*)
        FROM [SessionDeliveryParticipant] AS sub2
        WHERE sub2.SessionDeliveryCalendarID = [SessionDeliveryParticipant].SessionDeliveryCalendarID
    ) THEN 1
    ELSE 0

Thanks