SBS 2008 can browse shares, but not connect to any

I have an SBS 2008 machine which is causing me headaches.

For Windows shares, it seems to be living in its own little isolated world. It can browse a list of network shares just fine (NET VIEW), but it refuses to connect to any, with:

\\storage\shared is not accessible. You might not have permission to use this network resource. Contact the administrator of this server to find out if you have access permissions.

The specified network name is no longer available.

And the same goes for every other computer on the network. They can view the shares on the SBS 2008 server, but they cannot connect to any. they get the same message.

I don't know how long this has been going on for, and it may have been going on since the server was first deployed.

Additional information:

• It's just a vanilla configuration, without any additional software installed
• It's not the Symantec Endpoint Protection issue (but the symptoms are very similar).
• There are no errors in the event logs that I can find.
• The "Computer Browser" service is disabled. I don't know if this is normal or not, but enabling it seemed to make no difference.
• Everything else (like Exchange, SQL Server) is all running fine and does not experience any connectivity issues
• The ForeFront subscription has expired (probably not relevant)

There is a concerning part of DCDIAG which I've outputted below (we only have one DC in one site, so I'm not sure if NTDS issues would be affecting this problem):

 Starting test: Services
       Could not open NTDS Service on EPPINGDC, error 0x5 "Win32 Error 5"
    ......................... EPPINGDC failed test Services
 Starting test: SystemLog
    An Error Event occurred.  EventID: 0x00000457
       Time Generated: 08/22/2010   07:40:19
       EvtFormatMessage failed, error 15100 Win32 Error 15100.
       (Event String (event log = System) could not be retrieved, error
       0x3afc)
    An Error Event occurred.  EventID: 0x00000457
       Time Generated: 08/22/2010   07:40:27
       EvtFormatMessage failed, error 15100 Win32 Error 15100.
       (Event String (event log = System) could not be retrieved, error
       0x3afc)
    ......................... EPPINGDC failed test SystemLog

Any suggestions?

I just had another thought. I've seen a server in the past where the IPC$ share somehow disappeared. Check your shares to make sure it's still there. If it isn't, run net use IPC$

Also let us know how the BPA changes worked out for you.

EDIT

All right. I have another suggestion. Reset winsock and TCP/IP. You'll probably want to be onsite for this. You have to reset the IP address afterwards (A good idea is to rerun the "Connect to internet" wizard when you're done). Here's the commands:

netsh winsock reset c:\winsockreset.log
netsh int ip reset c:\ipreset.log