Sorry, but we are not clairvoyants and therefore can't help with the little information posted by you.
UltraEdit for Windows v12.20b was released 2007, i.e. 10 years ago. There have been changes in the last 10 years, not only in UltraEdit, but also for protocols like FTP and SFTP. Especially the encryption algorithms as used by SFTP have changed in the last 10 years. I suppose the other FTP tools and the FTP server are much newer than the used version of UltraEdit.
Further you have whether posted the used url nor any information about the settings required by the FTP server (or is it an SFTP server) and what you have configured in UltraEdit's FTP account manager. We don't know anything about your network environment like active firewalls without or with exceptions for certain applications. You have not posted an FTP log as UltraEdit can output or a log made with Wireshark for analyzing the failed connection establishment.
So which advice should we give? What about making a backup of user configuration of UltraEdit v12.20b, i.e. creating a copy of directory %APPDATA%\IDMComp\UltraEdit or just rename that directory while UltraEdit is not running, then uninstall UE v12.20b and install currently latest version which is v24.10?