DDJ SZ CONNECTION ISSUE

My DDJ SZ won't connect to serato or rekordbox. There are two usb ports - A and B. A works fine. When I plug in to B, the lights on the controller flash as if it has recognized the connection, but serato and rekordbox do not respond at all, as if the controller was never plugged in. This is very frustrating because this was a key feature that I bought the controller for. Please help.