Hello,
I am trying to achieve the same thing and have the exact same error as you do. Could you please indicate if you solved your problem ?
I am trying to login with SSO to our SAP server. We already have a working SSO configuration using SAP GUI. I am using the v3 of the .Net connector in 64bits. My app is only made for x64 architecture (desktop app, not ASP). Logging manually works fine. My parameters are correct (SncMode,SncPartnerName,Client,SncMyName and SncLibraryPath)
Hint : Architecture doesn't seem to be a problem, I am pointing to the same directory as you, and it is indeed the 64bit version of sapcrypto.dll. If I change the path to the x86 Program Files dir, I get an error saying "Error 193 = "C:\Program Files (x86)\SAP\FrontEnd\SecureLogin\lib\sapcrypto.dll is not a valid Win32 application".
One other thing, on the SAP server side, tech tells me that we are indeed using Kerberos for SSO.