Host key Unverified

I have tried with mixed success to connect to several severs using the winscp assembly.
I occasionally run into servers when trying to connect I get error Host Key Unverified.
i had used Session.DefaultConfiguration = False on my session but that does not work every server.

Use SessionOptions.HostKey to set expected host key.
https://winscp.net/eng/docs/library_sessionoptions

Using Session.DefaultConfiguration is not recommended.