Thanks for the reply. As mentioned in my first email, FreeRDP does not work. The problem is that previously you could DOS a windows server because of the way in which the authentication worked. This problem is related to Network Authentication which is required for newer RDP connections which first requires a user to authenticate against the domain before starting the actual RDP session. With some changes WindowsXP can connect to such rdp servers as well as the client available on a mac.
On 15 June 2012 08:51, Beaumont, Kevin <Kevin.Beaumont@princes.co.uk>
I think that means the server requires NLA or SSL (TLS) to connect. Try using FreeRDP, it implements these.