I've never seen the error before.
Where are you getting it? How exactly are you running/using the .NET assembly?
I'm getting this error when I try to run WinSCP on some old Windows Server 2008.
Is there any older version that I could use? Any other suggestions?
I tried some solutions that I googled regarding permissions for .NET but nothing worked.
I don't have session log atm, but I will update post once I have it.
Update: Debug and session.log are not being generated at all. Just this error for assembly.