Just wanted to second what Shack posted above, as I had a similar issue. Downgrading to an older version of SimAppPro was a valid workaround. I never had to do any physical disassembly of the unit before, no reason to start now. The SimAppPro software has been generally solid, I'd give it a B/B+. But after all this time of having trouble free firmware updates, it's pretty clearly a Winwing software issue if suddenly support is telling us that we need to physically disassemble the unit to apply an update. I hope it doesn't crop up again, but this is almost certainly a problem on their end.
I did basically the same thing as Shack:
1) Uninstall existing SimAppPro
(If you are familiar / comfortable with Revo Uninstaller, I'd suggest using that to cleanup the SimAppPro registry leftovers, as the uninstall doesn't appear to be 100% clean)
2) Reboot then install older version of SimAppPro (1.8.18 was the oldest version I still had in my downloads folder)
3) Update all required firmware (I unplugged all other USB devices as requested, it complained that the base and stick were still connected but the application proceeded with the firmware updates). Repeated same steps for my throttle base / handle.
4) Update to latest version of SimAppPro
Hopefully this issue doesn't repeat itself, my sim pit did gather dust for about three months, so it might have just been a version mismatch... where I updated the application to a newer version after three months away... and that newer application version didn't play nice with existing firmware that was two or more releases out of date. That's just a guess, but it's the only additional circumstance I can come up with.