nesting "and" in sumproduct function
 

I need to nest a date range argument in a sumproduct function but can't seem
to get it to work. When I only write "...<=c1)" within the string, it works
for any data less than or equal to the cell's date, but I need to say
"...=x-date AND <=y-date...".

I'm sure its staring me in the face but...

Thanks for your help out there.

George