10.6 client will not connect to 10.5 server as portable home

I am trying to set up a snow leopard client with a portable home directory. The user can connect with macbook pro running 10.5 just fine. However, when the user tries to login from a new 10.6 machine, he gets the error: "You are able to log into the user account XXX at this time. Logging into the account failed because an error occurred" I have bound the 10.6 client to the server through the new "Prefs -> Users -> login" method. Any ideas?