I solved it by simply add the /certificate switch. Now all is fine.

You probably need this:
https://winscp.net/tracker/1646

I'm sending you an email with a development version of WinSCP to the address you have used to register on this forum.

Dear all,
I have trouble with WinScp. All I wanna do is to load a file up via Winscp.
I estabblished a connection and than I let WScp generate the script.

But everytime I startet the script, I got the option to acceppt the certifcate or not. If nothing done, the transfer breaks up. Always pressing yes is annoying. Is there a way to stop the options or to silence it or to make yes to default option?
Regards

oliver