Exchange 2013 CU18 install fails with ADObjectAlreadyExistsException

I'm updating from Exchange 2013 RTM to Exchange 2013 CU18.

Exchange upgrade is failing currently with the following error…

Microsoft Exchange Server 2013 Cumulative Update 18 Unattended Setup

Copying Files… File copy complete. Setup will now collect additional
information needed for installation. Languages Mailbox role: Transport
service Client Access role: Front End Transport service Mailbox role:
Client Access service Mailbox role: Unified Messaging service Mailbox
role: Mailbox service Management tools Client Access role: Client
Access Front End service

Performing Microsoft Exchange Server Prerequisite Check

Configuring Prerequisites                                 COMPLETED
Prerequisite Analysis                                     COMPLETED

Configuring Microsoft Exchange Server

Organization Preparation                                  FAILED
 The following error was generated when "$error.Clear();
    install-GlobalAddressLists -DomainController $RoleDomainController

" was run:
"Microsoft.Exchange.Data.Directory.ADObjectAlreadyExistsException: Ac
tive Directory operation failed on HOSTEX-1.mydomain.cloud. The object
'CN= Default Global Address List,CN=All Global Address
Lists,CN=Address Lists Contain er,CN=Hosted Exchange,CN=Microsoft
Exchange,CN=Services,CN=Configuration ,DC=mydomain,DC=cloud' already
exists. —> System.DirectoryServices.Protocols.
DirectoryOperationException: The object exists. at
System.DirectoryServices.Protocols.LdapConnection.ConstructResponse(Int32
messageId, LdapOperation operation, ResultAll resultType, TimeSpan
requestTimeOu t, Boolean exceptionOnTimeOut) at
System.DirectoryServices.Protocols.LdapConnection.SendRequest(DirectoryReq
uest request, TimeSpan requestTimeout) at
Microsoft.Exchange.Data.Directory.PooledLdapConnection.SendRequest(Directo
ryRequest request, LdapOperation ldapOperation, Nullable1
clientSideSearchTimeo ut, IActivityScope activityScope, String
callerInfo) at
Microsoft.Exchange.Data.Directory.ADDataSession.ExecuteModificationRequest
(ADObject entry, DirectoryRequest request, ADObjectId originalId,
Boolean emptyO bjectSessionOnException, Boolean isSync) --- End of
inner exception stack trace --- at
Microsoft.Exchange.Data.Directory.ADDataSession.AnalyzeDirectoryError(Pool
edLdapConnection connection, DirectoryRequest request,
DirectoryException de, In t32 totalRetries, Int32 retriesOnServer)
at
Microsoft.Exchange.Data.Directory.ADDataSession.ExecuteModificationRequest
(ADObject entry, DirectoryRequest request, ADObjectId originalId,
Boolean emptyO bjectSessionOnException, Boolean isSync) at
Microsoft.Exchange.Data.Directory.ADDataSession.Save(ADObject
instanceToSa ve, IEnumerable1 properties, Boolean bypassValidation)
at
Microsoft.Exchange.Data.Directory.SystemConfiguration.ADConfigurationSessi
on.Save(ADConfigurationObject instanceToSave) at
Microsoft.Exchange.Management.Deployment.InstallGlobalAddressLists.CreateD
efaultGal(ADObjectId defaultGal) at
Microsoft.Exchange.Management.Deployment.InstallGlobalAddressLists.Interna
lProcessRecord() at
Microsoft.Exchange.Configuration.Tasks.Task.b__b()
at
Microsoft.Exchange.Configuration.Tasks.Task.InvokeRetryableFunc(String
fun cName, Action func, Boolean terminatePipelineIfFailed)".

The Exchange Server setup operation didn't complete. More details can
be found in ExchangeSetup.log located in the
:\ExchangeSetupLogs folder.

Any help at all is appriciated!