Identical item codes in two different warehouses

We currently have several items that exist in two warehouses. We are using SAP Business One, 8.81 PL09, DTW 88.1.7. All of our items from warehouse A have pulled without any errors. We are using a ItemGroupCode of 100 (default) for both warehouses, and managing the items by warehouse. Attempting to use DTW to pull the identical items into B, we receive an error of Item code 'ABC1234' already exists error 65171. My guess is that we will need to use a separate ItemGroupCode for each warehouse. I'm sure that other people out there have had the same issue. Thank you.