I am trying to find the average number of workdays between two named columns
(ActivityEnd and ReportComplete) in the month of January. It has to be an
array calculation because each row is a separate project. The following
produces a #VALUE! error, possibly because NETWORKDAYS won't work with arrays.

{=AVERAGE((NOT(ISBLANK(ActivityEnd)))*(NOT(ISBLANK (ReportComplete)))*(NETWORKDAYS(ReportComplete-ActivityEnd))*(MONTH(ActivityStart)=1))}

Can anyone offer a suggestion?

Thanks,
Cassandra