My network has about 20 Windows XP clients. It often happens that a client can't access the shared folders in the Windows 2003 Server that I have; that happens right after logging in. It gives me a "you don't have permission for that resource" error, even though the client has been authenticated by the server. I can fix that in the client by disabling and enabling the network connection. Once I do that, I can access the AD normally.
My network setup is fairly simple: I have a pfsense box that runs dns and dhcp and I the win 2003 server takes care essentially of the AD and shared resources (files and printers).