I have owned the FX-4A for almost a year now, I have never seen that error message. I wonder if you have a newer or older firmware than I do. It does sound like high SWR to me. BTW, I really like my FX-4A and use it everyday. I also have the LD-5 which just sits on a shelf. The LD-5 is nice and all, I just prefer the form factor of the FX-4A better.
There is a note in the manual that directs to enter a value in the configuration of 20. After I did that, I stopped getting the warning. I still am having trouble getting my first QSO. I read somewhere that I need to increase the gain via a set screw on he board. I’m looking for that now. Have you had problems wit low modulation?
A lot of people had to turn their mic gain up on the inside, but I didn’t have to do it on mine. It’s pretty easy to do if you take it apart. BTW, I know of the setting you are talking about, I have mine set at 20 also.