I have a USB DMX product called DMXking ultraDMX RDM Pro (I've also tried the DMXking ultraDMX Micro, same issue) and I'm using the free software FreeStyler and trying to figure out how to get it to work. These products are for controlling DMX light fixtures.
Select either DMXking USB DMX512-A or Enttec Pro. Do not choose ultraDMX Pro unless you are actually using this device. Also make sure you've selected the right COM port, plus make sure the latest driver from FTDI Chip is installed (FTDI Drivers). A good practice is to use the ultraDMX Configuration Utility to help locate this if necessary. Sometimes FreeStyler gives an error message during device selection, just restart it.