I'm running Server 2012 R2 and XCTU Version: 6.3.0. I was able to get the "Add Radio Module" and "Discover Radio Module" options working correctly. Here's how:
Right-click on the XCTU icon and select "Troubleshoot compatibility." From there, select "Try Recommended Settings." For me, "Windows Compatibility Mode:Windows 7" was the recommended setting. From there click the "Test the program..." button and XCTU launched. Leave the troubleshooter window open while testing out XCTU. I was able to use XCTU correctly from that point forward. Once you've verified everything works, close the program and go back to the troubleshooter window and click the "Next" button. Click on "Yes, save these settings for this program" option and then the "Close" button. Now when you launch XCTU, everything should work correctly.