Sumproduct gives Value error

Edit:

=SUMPRODUCT((Sheet2!A3:A5=A3)*(Sheet2!C1:D1=B2),Sheet2!C3:D5*N(Sheet2!F2)/60)
+SUMPRODUCT((Sheet3!A3:A5=A3)*(Sheet3!C1:D1=B2),Sheet3!C3:D5*N(Sheet3!F2)/60)
+SUMPRODUCT((Sheet4!A3:A5=A3)*(Sheet4!C1:D1=B2),Sheet4!C3:D5*N(Sheet4!F2)/60)

Thanks....
it's now working...though not sure what the 'N' purpose is...