Kerberized NFS root user access

[steve]

Hi
openSUSE 12.1

Our Samba4 DC has a Kerberised NFS mounted share. I need the root user 
to be able to write to the share. I can do this with by mounting it with:
no_root_squash,sec=sys

Is there any way I can do it with:
sec=krb5

root has a ticket in /tmp/krb5cc_0 but he always gets permission denied 
when the share is mounted krb5, even with the no_root_squash

Cheers,
Steve