Copying files to remote side failed. Can't open that file: Permission denied

I have been trying to troubleshoot why my script isn't working, but today I tried to just upload the file manually. No luck - I get the response: "Copying files to remote side failed.
Can't open that file: Permission denied"

Using WinSCP 5.15.5 on Win7, via FTP using gui and/or script.

I have tried to set the permissions for the file in Windows, but it made no difference.

The error comes from the server. The server does not allow you to create the file. Please ask your server administrator.