I did some tests to rule out any problems on our end and as far as I can tell everything appears to be fine.
There are two situations that can result in the error message you are seeing.
1. A unknown software/hardware issue has caused the FlashFXP.exe program file to be come corrupted on your drive.
2. A malicious program is running on your computer and it has modified the FlashFXP.exe.
Are you using any anti-virus software? if so which? is it up to date?
The easiest way to determine if the problem is #2 is to re-install FlashFXP.
When running the installer for the same version as installed you need to select the "repair" option.
You can download FlashFXP directly from the following link
http://get.flashfxp.com/ftp/client/d...XP44_Setup.exe
Many features will fail or simply not function when the digital signature check fails this is by design.