We are having a similar problem.
We have a customer Web Application solution running on an IIS server for which we require SNC-based SSO connection for RFC via .Net Connector 3.0
In our experience the gx64krb5.dll works effectively.
However, the customer has recently upgraded and only sapcrypto.dll library works for sso integration.
This works for us with a direct RFC connection, but does not appear to support Kerberos delegation.
Can anyone confirm whether they have successfully employed sapcrypto.dll with Kerberos delegation for SSO for RFC integration?
The specific error message we are getting is:
LOCATION CPIC (TCP/IP) with Unicode ERROR GSS-API(maj): No credentials were supplied Unable to establish the security context target="p:S=SL-ABAP-TRD@SITE.XXX.COM.AU" TIME Mon Jun 27 09:55:59 2016 RELEASE 721 COMPONENT SNC (Secure Network Communication) VERSION 6 RC -4 MODULE sncxxall.c LINE 3604 DETAIL SncPEstablishContext SYSTEM CALL gss_init_sec_context COUNTER 8
Regards
Richard