Hi, Stacey-
I suspect Excel is still looking at column E as if it is a date. You
can use the MONTH() function, which returns a number from 1 to 12,
against a date. Your formula would look like this:
=SUMPRODUCT(--('PO LIST'!H3:H88="Calibration"),--(Month('PO
LIST'!E3:E88)=1),('PO LIST'!C3:C88))

Let us know if this works!

Dave O