Which version of UltraEdit do you use on which operating system?

An old version of UltraEdit respectively of the wodFtpDLX library used by UltraEdit is perhaps not compatible with the encryption technology used by the SFTP server.

What do you have configured in FTP Account Manager on all tabs for this SFTP server?

Do you have enabled at Advanced - Settings or Configuration - FTP and the configuration setting Show FTP log in output window and looked on FTP log in output window?

It could be that wodFtpDLX library used by UltraEdit is corrupted on hard disk. An uninstall and reinstall of UltraEdit without deactivation of license and without deletion of user configuration might help to fix this problem. Just uninstall the program files of UltraEdit, restart Windows to really complete the uninstall (shell extension DLLs can be only deleted while Windows is not running)  and install UltraEdit again.

Thanks for the additional data about your environment.

OpenSSH 7.1p1 was released 2015-08-21.
UltraEdit version 14.10.0.1025 was released 2008-07-30. I have not archived version 14.10.0.1018.
Currently newest PuTTY version 0.71 was released on 2019-03-16 which I assume is used by you.

Do you really think nothing changed between July 2008 and August 2015 (seven years!) regarding to encryption technologies for SSH File Transfer Protocol?

Many encryption algorithms were added between July 2008 and August 2015 as it can be read in OpenSSH release notes or in PuTTY change log or in release notes of wodFtpDLX which is the library used by UltraEdit for FTP/SFTP/SSH/Telnet. So I suppose an incompatibility in SSH encryption between wodFtpDLX version used by UltraEdit version 14.10.0.1018 and OpenSSH 7.1p1 used by the SFTP server.

My recommendation is paying for an upgrade to currently latest UltraEdit v26.10.0.38 which is installed with latest available version of wodFtpDLX.

I have helped once a user to update just the three files wodCertificate.dll, wodFtpDLX.dll and wodTelnetDLX.ocx installed with UE v16.30 by the three files with same name installed with 32 bit UE v24.20, see my post on UltraEdit for Windows v16.xx won't connect to Raspberry Pi with SSH (solved) for details.

But I really doubt that wodCertificate.dll (DLL version 1.7.6.5), wodFtpDLX.dll (DLL version 3.5.5.755) and wodTelnetDLX.ocx (DLL version 2.5.6.179) of 32 bit UltraEdit version 26.10.0.38 are 100% compatible with wodCertificate.dll (DLL version 1.4.0.4), SftpDLL.dll (DLL version 3.2.3.73) and wodTelnetDLX.ocx (DLL version 2.3.6.107) of UltraEdit version 14.10.0.1018. With UltraEdit v14.20 the DLL file SftpDLL.dll with wodSFTP API library was replaced by DLL file wodFtpDLX.dll (DLL version 2.8.6.439) with wodFtpDLX Component library. So I am quite sure that the library files of 32 bit UE v26.10.0.38 for FTP/FTPS/SFTP are not compatible with the library files of UE v14.10.0.1018, especially because of one library is a completely different one.

I think, there is no chance to get UltraEdit v14.10.0.1018 working with your SFTP server because this version of UltraEdit is really too old.

Well, if SFTP is working or is not working with very old UltraEdit v14.10.0.1018 depends on which encryption algorithms the SFTP server requires as supported by SFTP clients.

For example support for AES128-CTR, AES192-CTR, AES 256-CTR encryption algorithms in SSH2 protocol was added in version 3.0.7 of wodFtpDLX library released July 20, 2010 and is for that reason definitely not supported by different and much older wodSFTP API library installed with UltraEdit v14.10.0.1018. The key exchange algorithms ECDH-SHA2-NISTP256, ECDH-SHA2-NISTP384, ECDH-SHA2-NISTP521 and the signature algorithms ECDSA-SHA2-NISTP256, ECDSA-SHA2-NISTP384, ECDSA-SHA2-NISTP521 are supported by wodFtpDLX library since version 3.5.0 released September 17, 2015. So these newer algorithms are also not supported by wodSFTP API library installed with UltraEdit v14.10.0.1018.

SSH, SSH2 and SSH3 define each a set of encryption, key exchange and signature algorithms. Which of these algorithms a server requests as being supported by clients depends on server configuration.