Server 2008 randomly disappears from network browse list

A customer's servers (SBS2011 and Server 2008 R2) sometimes stop showing up in the network browse list.
All workstations are Windows 7 Pro or ultimate 64bit.
You can still access the servers by manually typing in \\SERVERNAME in the search box.
Mapped drives stay mapped.
All internal firewalls have been disabled or turned off.
One minute, you will open Explorer, and click Network, and see a complete list of all workstations and servers.  Then, at a random time, you open explorer and click network, and all you can see are the workstations.
When running a net view command on the command prompt, if the servers are not showing up in explorer, you get "Operating system error 71.

 No more connections can be made to this remote computer at this time because there are already as many connections as the computer can accept. "

Troubleshooting:
I have tried stopping and disabling Computer Browser service on both servers and workstations - no effect.
All computers have network Discovery set to ON.
On the SBS2011 server, the BPA shows no problems.
DCDIAG shows all tests passed.
Re-verified all firewalls OFF

This is really killing me, as I have already opened another question and closed it.  Thought it was resolved via updates, but it was the intermittent nature of the problem that fooled me into thinking it was resolved.  Old questions is here:  http://www.experts-exchange.com/OS/Microsoft_Operating_Systems/Server/Q_28260322.html
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Digital_SkreamAsked:
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Digital_SkreamConnect With a Mentor Author Commented:
Since nobody knows the answer, I will be taking this up with Microsoft on a paid support basis.  Hopefully they will be able to fix the problem.
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Andrej PirmanCommented:
Hmmm...
Check this registry key out on problematic server - might be blocking anonymus requests playing some role:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\LSA

Add new value under that key:
Value Name: RestrictAnonymous
Data Type: REG_DWORD
Value: 2
Default: 0
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Digital_SkreamAuthor Commented:
That key's current value is 0, which does not put any restrictions on anonymous enumeration of resources, as per TechNet.
http://technet.microsoft.com/en-us/library/bb418944.aspx
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WORKS2011Austin Tech CompanyCommented:
what happens if you do ipconfig /flushdns then try to connect?

Run dcdiang /test:dns and post the resutls
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Digital_SkreamAuthor Commented:
There is never any problem trying to connect.  Typing \\servername will bring up that server's resources as if I had browsed to it.
Ipconfig/flushdns has no effect whatsoever.
Here are the results of a dcdiag /test:dns
You will notice that while it shows a warning about the ptr for 10.0.0.127, it still passes all DNS tests, and indeed even Microsoft states that warning is "no big deal".

C:\Users\Administrator>dcdiag /test:dns

Directory Server Diagnosis

Performing initial setup:
   Trying to find home server...
   Home Server = DCSERVERNAME
   * Identified AD Forest.
   Done gathering initial info.

Doing initial required tests

   Testing server: Default-First-Site-Name\DCSERVERNAME
      Starting test: Connectivity
         ......................... DCSERVERNAME passed test Connectivity

Doing primary tests

   Testing server: Default-First-Site-Name\DCSERVERNAME

      Starting test: DNS

         DNS Tests are running and not hung. Please wait a few minutes...
         ......................... DCSERVERNAME passed test DNS

   Running partition tests on : ForestDnsZones

   Running partition tests on : DomainDnsZones

   Running partition tests on : Schema

   Running partition tests on : Configuration

   Running partition tests on : domain

   Running DCSERVERNAME tests on : domain.local
      Starting test: DNS
         Summary of test results for DNS servers used by the above domain controllers:

            DNS server: 128.8.10.90 (d.root-servers.net.)
               1 test failure on this DNS server
               PTR record query for the 1.0.0.127.in-addr.arpa. failed on the DNS server 128.8.10.90
         ......................... domain.local passed test DNS

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WORKS2011Austin Tech CompanyCommented:
Operating system error 71
my understanding means there are too many connections being made at once.

What happens when you check the connections made on the servers? I know on some servers I've seen the DNS open every available port and I had to manually disconnect them.

Have you run TCPview from sysinternals to see whats open.
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WORKS2011Austin Tech CompanyCommented:
On the servers go to Start / Administrative Tools / Share and Storage Management / on the right go to Manage Sessions check "# Open Files" may give an indication what's causing the error.
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Digital_SkreamAuthor Commented:
@WORKS2011
Yes, that error means too many connections - but this error is happening on the workstations, not on the server.

The servers each have an appropriate number of open files... one is a file server, the other an SBS (so, exchange).  Am not seeing outlandish values.
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chuckmcculloughCommented:
This might be a stretch, but have you tried troubleshooting browsing on your network? It's been a number of years since I used them, but there used to be two utilities for this: browmon, browstat. If they are still around I'm not sure how compatible they are with newer OSes such as Windows 7.

My thinking on this recommendation is you might have competing master browsers, or a workstation responding to browse requests, etc. The randomness could be caused by getting a browse list response from one server (or workstation), then later a different server offers up the list (with different results).

If one of your workstations is competing for the ability to keep browser lists that can cause issues, and you can disable this in the registry:

http://technet.microsoft.com/en-us/library/cc959923.aspx
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Digital_SkreamAuthor Commented:
@chuckmccullogh
I appreciate the response, however, the old computer browser service has been relegated to legacy systems.  Modern (2008 and later) server operating systems have ti disabled by default, and rather than the computer browser service, they utilize AD queries to generate the list of computers on the network.  And this network is entirely server 2008, sbs20122, and windows 7 pro/ultimate machines.  Computer browser has been disabled on all machines.
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WORKS2011Austin Tech CompanyCommented:
Computer browser has been disabled on all machines.
service is running on all my machines.

Computer Browser / Started / Automatic

What happens if you start them I've always seen them running.
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Digital_SkreamAuthor Commented:
No change.
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Digital_SkreamAuthor Commented:
Since nobody knows the answer, I will be taking this up with Microsoft on a paid support basis.  Hopefully they will be able to fix the problem.
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