Ahhh - I think I got it... I just added one more quotation after 'Data'!Z$2:Z$. So the final code looks like:

Range("R2").Formula = "=SUMPRODUCT(--('Data'!C$2:C$" & dLastRow & "=C2),--('Data'!I$2:I$" & dLastRow & "=H2),('Data'!Z$2:Z$" & dLastRow & "))"