It is returning a zero, I should be getting the number 4 since there are 4 people that are FT that are listed as REG or INTERIM at the OCC or RCC. Am I doing something wrong?
If the Location codes will always be RCC or OCC, you can use this alternative.
=SUMIFS(K2:K27,A2:A27,2016,B2:B27,"Dec",C2:C27,"Week 3",E2:E27,"?CC")
But again, as @Khalid NGO suggested, use either a pivot or SUMPRODUCT or SUMIFS as they will give you accurate results when you have more items in the data.