Some vendors still ship a version of RPC/NFS that allows at
most 8 groups in the client credentials. Root on Solaris is by
default in 10 groups. As a result, the Solaris 2.x mount
command will send AUTH_UNIX credentials that are too big to
cope with for the remote mount daemon resulting in the ``Invalid
client credential'' error.
Workaround: put root and all your users in 8 or less groups.
NOTE: You must logout and login again for changes in the number
of groups to take effect. (or exit root's shell and re-su)