Updating 2013 SP1 to CU8 Error - Set-SharedConfigDC Fails

Question

I have two 2012 servers running Exchange 2013 SP1. They are both multi-role servers and are members of a DAG and are also load-balanced behind a Citrix Netscaler. I was ready to begin moving my mailboxes from 2010 to 2013 when I ran into a problem. In order
to try and resolve this problem, I attempted to update to CU8.
(After a successful mailbox move, I am unable to open my own mailbox in Outlook (2013 or 2010). I receive an error that "the set of folders cannot be opened". I am, however, able to view my mailbox from another migrated mailbox which has "full
access" to it. After some unsuccessful attempts to figure it out, I decide that I should probably update Exchange to the latest before I start messing with other things. Bad mistake.)
The CU8 setup fails in the Set-SharedConfigDC step with the error "No Minimal Required Number of Suitable Directory Servers Found in Forest".
I've read that I need IPv6 enabled. It had previously been "unchecked" in the NIC settings of the Exchange and DC servers. I've enabled it on the Exchange server and two of the DCs one of which is a GC. No luck. I've also added the "Exchange
Servers" and "Exchange Subsystem" groups to the AD "Administrators" group which was another suggestion I received.
The DCs are in a different subnet from the Exchange server.  I am running at domain functional level of 2003.
And just to reiterate: I had successfully installed Exchange 2013 SP1 with IPv6 "unchecked" on all Exchange and DC servers before the CU8 update failed.
-edit- Here's the relevant section of the log:
[04/01/2015 09:50:52.0841] [2] Active Directory session settings for 'Set-SharedConfigDC' are: View Entire Forest: 'True', Configuration Domain Controller: 'AC-DC1.mydomain.network', Preferred Global Catalog: 'AC-DC1.mydomain.network', Preferred Domain Controllers: '{ AC-DC1.mydomain.network }'
[04/01/2015 09:50:52.0841] [2] User specified parameters: -DomainController:'AC-DC1.mydomain.network' -ErrorVariable:'setSharedCDCErrors' -ErrorAction:'SilentlyContinue'
[04/01/2015 09:50:52.0841] [2] Beginning processing Set-SharedConfigDC
[04/01/2015 09:51:47.0056] [2] The call to Microsoft Exchange Active Directory Topology service on server 'TopologyClientTcpEndpoint (localhost)' returned an error. Error details No Minimal Required Number of Suitable Directory Servers Found in Forest mydomain.network Site Default-First-Site-Name and connected Sites..
[04/01/2015 09:51:47.0056] [2] No Minimal Required Number of Suitable Directory Servers Found in Forest mydomain.network Site Default-First-Site-Name and connected Sites.
[04/01/2015 09:51:47.0056] [2] The call to Microsoft Exchange Active Directory Topology service on server 'TopologyClientTcpEndpoint (localhost)' returned an error. Error details No Minimal Required Number of Suitable Directory Servers Found in Forest mydomain.network Site Default-First-Site-Name and connected Sites..
[04/01/2015 09:51:47.0056] [2] No Minimal Required Number of Suitable Directory Servers Found in Forest mydomain.network Site Default-First-Site-Name and connected Sites.
[04/01/2015 09:51:47.0071] [2] Ending processing Set-SharedConfigDC
[04/01/2015 09:51:47.0071] [2] Beginning processing Write-ExchangeSetupLog
[04/01/2015 09:51:47.0071] [2] An error ocurred while setting shared config DC. Error: The call to Microsoft Exchange Active Directory Topology service on server 'TopologyClientTcpEndpoint (localhost)' returned an error. Error details No Minimal Required Number of Suitable Directory Servers Found in Forest mydomain.network Site Default-First-Site-Name and connected Sites..
[04/01/2015 09:51:47.0071] [2] Ending processing Write-ExchangeSetupLog
[04/01/2015 09:51:47.0087] [2] Beginning processing Write-ExchangeSetupLog
[04/01/2015 09:51:47.0087] [2] Waiting 30 seconds before attempting again.
[04/01/2015 09:51:47.0087] [2] Ending processing Write-ExchangeSetupLog
[04/01/2015 09:52:17.0100] [2] Active Directory session settings for 'Set-SharedConfigDC' are: View Entire Forest: 'True', Configuration Domain Controller: 'AC-DC1.mydomain.network', Preferred Global Catalog: 'AC-DC1.mydomain.network', Preferred Domain Controllers: '{ AC-DC1.mydomain.network }'
[04/01/2015 09:52:17.0100] [2] User specified parameters: -DomainController:'AC-DC1.mydomain.network' -ErrorVariable:'setSharedCDCErrors' -ErrorAction:'SilentlyContinue'
[04/01/2015 09:52:17.0100] [2] Beginning processing Set-SharedConfigDC
[04/01/2015 09:53:11.0367] [2] The call to Microsoft Exchange Active Directory Topology service on server 'TopologyClientTcpEndpoint (localhost)' returned an error. Error details No Minimal Required Number of Suitable Directory Servers Found in Forest mydomain.network Site Default-First-Site-Name and connected Sites..
[04/01/2015 09:53:11.0367] [2] No Minimal Required Number of Suitable Directory Servers Found in Forest mydomain.network Site Default-First-Site-Name and connected Sites.
[04/01/2015 09:53:11.0367] [2] The call to Microsoft Exchange Active Directory Topology service on server 'TopologyClientTcpEndpoint (localhost)' returned an error. Error details No Minimal Required Number of Suitable Directory Servers Found in Forest mydomain.network Site Default-First-Site-Name and connected Sites..
[04/01/2015 09:53:11.0367] [2] No Minimal Required Number of Suitable Directory Servers Found in Forest mydomain.network Site Default-First-Site-Name and connected Sites.
[04/01/2015 09:53:11.0367] [2] Ending processing Set-SharedConfigDC
[04/01/2015 09:53:11.0382] [2] Beginning processing Write-ExchangeSetupLog
[04/01/2015 09:53:11.0382] [2] An error ocurred while setting shared config DC. Error: The call to Microsoft Exchange Active Directory Topology service on server 'TopologyClientTcpEndpoint (localhost)' returned an error. Error details No Minimal Required Number of Suitable Directory Servers Found in Forest mydomain.network Site Default-First-Site-Name and connected Sites..
[04/01/2015 09:53:11.0382] [2] Ending processing Write-ExchangeSetupLog
[04/01/2015 09:53:11.0382] [2] Beginning processing Write-ExchangeSetupLog
[04/01/2015 09:53:11.0382] [2] Waiting 30 seconds before attempting again.
[04/01/2015 09:53:11.0398] [2] Ending processing Write-ExchangeSetupLog
[04/01/2015 09:53:41.0412] [2] Beginning processing Write-ExchangeSetupLog
[04/01/2015 09:53:41.0412] [2] [ERROR] Unable to set shared config DC.
[04/01/2015 09:53:41.0412] [2] [ERROR] Unable to set shared config DC.
[04/01/2015 09:53:41.0412] [2] Ending processing Write-ExchangeSetupLog
[04/01/2015 09:53:41.0428] [1] The following 1 error(s) occurred during task execution:
[04/01/2015 09:53:41.0428] [1] 0. ErrorRecord: Unable to set shared config DC.
[04/01/2015 09:53:41.0428] [1] 0. ErrorRecord: System.Exception: Unable to set shared config DC.
at Microsoft.Exchange.Configuration.Tasks.Task.WriteError(Exception exception, ErrorCategory category, Object target, Boolean reThrow, String helpUrl)
at Microsoft.Exchange.Configuration.Tasks.Task.WriteError(Exception exception, ErrorCategory category, Object target)
at Microsoft.Exchange.Management.Deployment.WriteExchangeSetupLog.InternalProcessRecord()
at Microsoft.Exchange.Configuration.Tasks.Task.<ProcessRecord>b__b()
at Microsoft.Exchange.Configuration.Tasks.Task.InvokeRetryableFunc(String funcName, Action func, Boolean terminatePipelineIfFailed)
[04/01/2015 09:53:41.0428] [1] [ERROR] The following error was generated when "$error.Clear();
$maxWait = New-TimeSpan -Minutes 8
$timeout = Get-Date;
$timeout = $timeout.Add($maxWait);
$currTime = Get-Date;
$successfullySetConfigDC = $false;
while($currTime -le $timeout)
$setSharedCDCErrors = @();
try
Set-SharedConfigDC -DomainController $RoleDomainController -ErrorVariable setSharedCDCErrors -ErrorAction SilentlyContinue;
$successfullySetConfigDC = ($setSharedCDCErrors.Count -eq 0);
if($successfullySetConfigDC)
break;
Write-ExchangeSetupLog -Info ("An error ocurred while setting shared config DC. Error: " + $setSharedCDCErrors[0]);
catch
Write-ExchangeSetupLog -Info ("An exception ocurred while setting shared config DC. Exception: " + $_.Exception.Message);
Write-ExchangeSetupLog -Info ("Waiting 30 seconds before attempting again.");
Start-Sleep -Seconds 30;
$currTime = Get-Date;
if( -not $successfullySetConfigDC)
Write-ExchangeSetupLog -Error "Unable to set shared config DC.";
" was run: "System.Exception: Unable to set shared config DC.
at Microsoft.Exchange.Configuration.Tasks.Task.WriteError(Exception exception, ErrorCategory category, Object target, Boolean reThrow, String helpUrl)
at Microsoft.Exchange.Configuration.Tasks.Task.WriteError(Exception exception, ErrorCategory category, Object target)
at Microsoft.Exchange.Management.Deployment.WriteExchangeSetupLog.InternalProcessRecord()
at Microsoft.Exchange.Configuration.Tasks.Task.<ProcessRecord>b__b()
at Microsoft.Exchange.Configuration.Tasks.Task.InvokeRetryableFunc(String funcName, Action func, Boolean terminatePipelineIfFailed)".
[04/01/2015 09:53:41.0428] [1] [ERROR] Unable to set shared config DC.
[04/01/2015 09:53:41.0428] [1] [ERROR-REFERENCE] Id=AllADRolesCommonServiceControl___ee47ab1c06fb47919398e2e95ed99c6c Component=EXCHANGE14:\Current\Release\Shared\Datacenter\Setup
[04/01/2015 09:53:41.0428] [1] Setup is stopping now because of one or more critical errors.
[04/01/2015 09:53:41.0428] [1] Finished executing component tasks.
[04/01/2015 09:53:41.0522] [1] Ending processing Install-BridgeheadRole
[04/01/2015 10:25:25.0150] [0] CurrentResult setupbase.maincore:396: 0
[04/01/2015 10:25:25.0150] [0] End of Setup
[04/01/2015 10:25:25.0150] [0] **********************************************

Answer 1

That might have done it!  I've marked your response as the answer although I do have some follow-up questions below.
I added MinSuitableServer = "1" under the line MinPercentageOfHealthyDC = "50" in the file "microsoft.exchange.directory.topologyservice.exe.config" in the CU8 setup folders. The setup still failed so I then edited the same file
in the existing Exchange directory and then rebooted. Setup then finished.
I still have my other Exchange server to do. I will make the same NIC changes and the same config file changes before attempting to run setup. I assume I should move the active DAG copy to the server that finally updated before proceeding but should I be wary
since the exchange servers are now on different versions?
Is there any explanation as to why this might have happened? I just can't understand why the initial setup succeeded back in January while this CU failed...