I always have trouble setting up sumproduct functions.

I have a sheet called "diary". In column I, i have diary codes (505, 510,
ect.). In column C, i have number codes that break down each diary code
(1-8). I want to count how many of each number code, i have for each diary
code. I'm using this function, but it returns an error. What am i doing
wrong?

=SUMPRODUCT((diary!I:I="510")+(diary!C:C="6"))