It looks like you are trying to use the SAP Cryptolib as the SNC library, which only supports Kerberos protocol (with proprietary SNC name format) and x.509 certificates for incoming SNC connections, and x.509 certificates for outbound connections.
So, you need to use an SNC library on the .net server that supports Kerberos protocol for outbound connections, and an SNC library on the server running SAP NetWeaver that supports Kerberos for incoming connections.