Leopard for home folders

I'm using leopard for home folders, both windows and mac. Until a couple of days ago I could access the shares via UNC path, ie. \\servername\sharename Now, from a windows box I have to use the ip address of the mac server. If I try mapping to the server name, it requests the Active Directory credentials but fails to authenticate. If I use the IP address, it maps just fine. Any thoughts?