Save Sound and Export Wave don't work!
I use rfxgen_v2.5_win_x64.
It's on my list for review!
I reviewed rFXGen and I couldn't find any issue. I was able to save/load .rfx files with no problem, as well as export .wav in different wave formats. I tested it on Windows 10. Where did you tried to save the files? Maybe it's a permissions issue.