I've had success with Authen::Krb 1.2 and MIT Krb5-1.2.2 on solaris 8. AuthenKrb 1.1 gave me the sv_undef problems, 1.2 didn't.

don't really know about KerbNet.

krb5_cc_default_name is supposed to return the name of your default credentials cache, try setting the KRB5CCACHE environment variable to your cache. Mine follows the /tmp/krb5cc_$UID format.