The remote FreeBSD host is missing a security-related update.
Simon Tatham reports : This version fixes a security hole in previous versions of PuTTY, which can allow a malicious SFTP server to attack your client. If you use either PSCP or PSFTP, you should upgrade. Users of the main PuTTY program are not affected. (However, note that the server must have passed host key verification before this attack can be launched, so a man-in-the-middle shouldn't be able to attack you if you're careful.)