Thanks for the review! I tried various directories to save the files and I don’t think it’s permission issue. I tried saving on desktop, a folder in desktop, a folder in D: disk. I also tried running the app as administrator but that didn’t help too.
I'm afraid I have no idea why it doesn't work for you. Fortunately, rFXGen is an open-source project, you can try to compile the code yourself and check for the issue with a debugger. A preconfigured Visual Studio 2022 solution as well as a plain Makefile are provided.