It seems that you didn't attach the logs.
Is the local or the remote file in use?
Anyway, WinSCP does not detect anyhow that the file is in use on either side. If it fails with "file in use", then it is the OS (local or remote) that think the file is in use. And it most likely indeed is. It might be temporary. It can be an antivirus application for example. If this is the case, all you can do is to retry bit later.

Hi,

We are using C# code to transfer an Access DB from an internal server on the domain to an external server in the DMZ. Intermittently this is failing and says the file we are copying is it use when it isn't. The file is quite large 759 MB.

I attach the WinSCP logs from the sending machine and FTP logs from the server that is receiving the files.

I can share the code if that helps..

Many thanks
Ben