Lets break down this error:

Error: Error when using WinSCP to upload files: WinSCP.SessionLocalException: The version of: C:\Program Files (x86)\WinSCP\WinSCP.exe (5.19.6.0) does not match version of this assembly

C:\Windows\Microsoft.Net\assembly\GAC_MSIL\WinSCPnet\v4.0_1.8.3.11933__2271ec4a3c56d0bf\WinSCPnet.dll (5.19.5.0).

As you see: One file path has (5.19.6.0) and the other file path has (5.19.5.0)

You need to have matching version .dll files in both paths.

Plus I would make sure your project has matching dll files also.