using window_sum returns 'all fields must be aggregates or constants while using table calculations from multiple data sources' even when calculated field does not involve fields from different data sources.

When i use a calculated field:

if

attr(event year)=attr({max(event year)})

then window_sum(subscribers,-(day(event date)),0)

end

it returns 'all fields must be aggregates or constants while using table calculations from multiple data sources' and here all my fields are from the same data source. What is the problem and how can i solve it?