We have some 2008 R2 servers that cannot browse the shares of a 2003 box when using "\\server1". It will open the shares when using "\\ipaddress" and "\\server1.domain". I can ping the 2003 server by ip address, NetBIOS name, and DNS name. They all resolve to the right IP address. We have other 2008 R2 servers and they are able to browse by NetBIOS name without any problems. The strangest thing, is that a reboot can temporarily "fix" the problem but it reoccurs within a few days. Any user that logs on to the server cannot map drives to that 2003 server but can browse to all other servers on the network. The 2003 server can browse the 2008 R2 servers by all 3 means; IP address, NetBIOS name, and long domain name format. UAC is disabled on all 2008 R2 servers. The 2003 server appears in entire network but we cannot double click it to open its shares.