Exchange 2013 AD prep- "Object reference not set to an instance of an object."

Hi

I am trying to install Exchange 2013 CU 3. We currently have CU 2 installed. During preparing the organization i get the error "Object reference not set to an instance of an object."

I googled this and some posts suggest its a dodgy exchange federation relationship. We don't have any or have it enabled.

Any ideas please?

Thanks

[01/05/2014 13:05:49.0656] [2] Group CN=Managed Availability Servers,OU=Microsoft Exchange Security Groups,OU=IT System,OU=Groups & Other Accounts,DC=domain,DC=local already exists.
[01/05/2014 13:05:49.0718] [2] [ERROR] Object reference not set to an instance of an object.
[01/05/2014 13:05:49.0718] [2] [WARNING] An unexpected error has occurred and a Watson dump is being generated: Object reference not set to an instance of an object.
[01/05/2014 13:05:50.0591] [1] The following 1 error(s) occurred during task execution:
[01/05/2014 13:05:50.0591] [1] 0.  ErrorRecord: Object reference not set to an instance of an object.
[01/05/2014 13:05:50.0591] [1] 0.  ErrorRecord: System.NullReferenceException: Object reference not set to an instance of an object.
   at Microsoft.Exchange.Management.Tasks.InitializeExchangeUniversalGroups.CreateOrMoveEWPGroup(ADGroup ewp, ADOrganizationalUnit usgContainer)
   at Microsoft.Exchange.Management.Tasks.InitializeExchangeUniversalGroups.InternalProcessRecord()
   at Microsoft.Exchange.Configuration.Tasks.Task.<ProcessRecord>b__8()
   at Microsoft.Exchange.Configuration.Core.LatencyTrackerExtension.StartAndEndInternalTracking(LatencyTracker latencyTracker, String groupName, String funcName, Boolean logDetailsAlways, Action action)
   at Microsoft.Exchange.Configuration.Core.CmdletLatencyTracker.StartAndEndInternalTracking(Guid cmdletUniqueId, String groupName, String funcName, Boolean logDetailsAlways, Action action)
   at Microsoft.Exchange.Configuration.Tasks.Task.<ProcessRecord>b__7()
   at Microsoft.Exchange.Configuration.Core.LatencyTrackerExtension.StartAndEndInternalTracking(LatencyTracker latencyTracker, String groupName, String funcName, Boolean logDetailsAlways, Action action)
   at Microsoft.Exchange.Configuration.Core.CmdletLatencyTracker.StartAndEndInternalTracking(Guid cmdletUniqueId, String groupName, String funcName, Boolean logDetailsAlways, Action action)
   at Microsoft.Exchange.Configuration.Tasks.Task.ProcessRecord()
   at System.Management.Automation.CommandProcessor.ProcessRecord()
[01/05/2014 13:05:50.0607] [1] [ERROR] The following error was generated when "$error.Clear(); 
	initialize-ExchangeUniversalGroups -DomainController $RoleDomainController -ActiveDirectorySplitPermissions $RoleActiveDirectorySplitPermissions" was run: "Object reference not set to an instance of an object.".
[01/05/2014 13:05:50.0607] [1] [ERROR] Object reference not set to an instance of an object.
[01/05/2014 13:05:50.0622] [1] [ERROR-REFERENCE] Id=443949901 Component=
[01/05/2014 13:05:50.0622] [1] Setup is stopping now because of one or more critical errors.
[01/05/2014 13:05:50.0622] [1] Finished executing component tasks.
[01/05/2014 13:05:50.0638] [1] Ending processing Install-ExchangeOrganization