Hello, I am glad you like it. I am not sure why you experience that. What operating system are you using? And does the console (command prompt) open? - The level editor need some console input in order to work.
Try to take a look at this image: https://i.imgur.com/aSgdb0B.png - It should explain the process.
I hope it works for you :-)
I just remembered, there is also a manual within the DUGA folder called Manuals.txt. It has some information on how to use the editor, if you get stuck :-)