Why does a user show anonymous logon in win2k3 domain?

I am trying to add rights to a user in the domain and when I go to add him from the list there is a red arrow with [anonymous logon] beneath his username.

He is an authenticated user in AD and is logging in within the LAN so why is it showing this?

Even if I give him rights to certain shares, he still doesn’t have full control of them becasue of this, any ideas?