Transfer was successfully finished, but temporary transfer file … could not be renamed to target file name …

With SFTP protocol, when automatic transfer resume is enabled, WinSCP first uploads the file to a temporary file with .filepart extension. Only after the transfer is completed the file is renamed to its actual name.

For you the renaming failed, for which there are many possible reasons including:

• Your SFTP server does not support renaming files;
• There’s some process that takes the uploaded file away immediately, before WinSCP is able to rename it.
• There’s antivirus (or similar application) that starts inspecting the uploaded file, locking it while doing that, what conflicts with WinSCP attempt to rename the file.

To circumvent that, disable transfer resume/transfer to temporary filename.

• In GUI, go to Preferences > Transfer > Endurance and disable Transfer Resume / Transfer to Temporary Filename.
• In scripting, use -resumesupport=off with put command (or other command that triggered the upload).
• In .NET assembly, use TransferOptions.ResumeSupport property.