SAP GUI with Kerberos 5, SAP Linux, SNC for SSO

[jhouska]

Hi,

I'm trying to configure SSO between SAP GUI 6.40 (Windows) and SAP
6.40 (Red Hat). I followed the instructions at
http://help.sap.com/saphelp_nw04s/helpdata/en/44/0ebf6c9b2b0d1ae10000000a114a6b/content.htm
(but used libgssapi_krb5.so instead of gsskrb5.dll) but I have a
trouble:
The checkbox "enable secure network connection" in sap gui is grey and
I cannot check it. (I installed sapsso.msi and set SNC_LIB before).
How can I enable this option in SAP GUI?

Thank you very much,
Jindra