=SUMPRODUCT(--('Donor Data'!A:A>=DATE(2005,10,1)),--('Donor Data'!A:A<=DATE(2006, 9,30)),--('Donor Data'!B:B>=1),--('Donor Data'!B:B<=19.99),'Donor Data'!B:B)

you need to enclose in single quotes.. because of the space between the words.

Again, you should reconcider using SUMIFS instead or use a shorter defined absolute range.