Function 'FILTER' is not supported in this context...?

I get this:



and yet I am not using Function 'FILTER'. 

This is working just fine:

Due_this_quarter =
COUNTX(
FILTER(
FILTER(
FILTER(
RA_FINDING,
RA_FINDING[Due Year] = RA_FINDING[Current_Year]
),
RA_FINDING[Due Quarter] = RA_FINDING[Current_Quarter]
)
,
RA_finding[Status_ID] = 1
)
,
RA_finding[Finding_ID]
)

Doe anyone have any insight into this unexpected behaviour?