Biff,

I'm using Excel 2007. I changed the full column designation to a range to
avoid the text in the header, but I get the same error:

{=SUMPRODUCT(--(MONTH(Tickets!A2:A25000)=3),--(ISNUMBER(MATCH(Tickets!G:G,Staff!A:A,0))))}

I tried eyeballing the records for text but there are 25,000 of them. Is
there a way to test for text in a range?