If you cannot log in, use the Password Recovery tool with your registered email or Serial Number.
: Any "fix" or "crack" found on third-party sites for this build often contains malware. Given that the software is no longer updated, using unauthorized "fixes" leaves your system and server credentials highly vulnerable to theft. Critical Review & Verdict FlashFXP v5.0 version history - Windows FTP Client
: Fixed a bug where a previously saved "Key-based" login would still be attempted even after changing the site profile to "Normal" login. Current Software Status
If you already have a working installation, Build 3956 introduced several targeted fixes: Remote Session Optimization