This issue will be seen if port 139 is blocked or filtered on any intermediate network or firewall devices. Often network administrators will block access to the NetBIOS over TCP/IP (NetBT) session port 139 and allow access only to SMB Direct Host port 445. This will also occur if NetBT is disabled on the remote Windows Vista client. Due to a problem with the initial release of Windows Vista, RAS connections will only succeed on port 139.
SMB is the file sharing protocol used by Windows. By default it should try to connect on both legacy NetBT port 139 and SMB Direct Host port 445. The problem is seen because Vista RTM does not add the RAS adapter GUID for SMB to the lanmanserver, lanmanworkstation, and SMB registry keys. Because of this if NetBT port 139 is blocked, file sharing will fail over a RAS interface.
For SMB to work over a RAS interface, the interface GUID must be added to the following registry locations:
To resolve this issue, see KB article 933468 - You cannot access SMB shares on a corporate network through a Remote Access Service (RAS) connection from a computer that is running Windows Vista
You can submit an online request for a hotfix to apply, or use the steps provided in the article to bind the SMB protocol to the RAS interface. Alternately you can apply Service Pack 1 for Windows Vista.
Here are the download links to obtain Vista SP1:
KB935791 - How to obtain the latest Windows Vista service pack:http://support.microsoft.com/kb/935791