Exchange 2016 – Tried to create new default OAB but the object already exists

To play arround with some NTLM/Kerberos authentication over NetScaler I needed to install a new Exchange 2016 server in my lab environment.

The  Exchange setup (CU5) was crashing with the following error message. All prerequisites like AD prep and UCMA installation have been done.


Der folgende Fehler wurde generiert, als "$error.Clear();
if (!$RoleIsDatacenter -and !$RoleIsDatacenterDedicated)
{
$createNewOab = $false;
$oabName = $null;
$oabAddressList = $null;
$oabVdirs = $null;
$oabGlobalWebDistribution = $false;
$oabConfiguredAttributes = $null;

Write-ExchangeSetupLog -Info ("Looking for an existing default OAB");
$defaultOab = Get-OfflineAddressBook -DomainController:$RoleDomainController | where {$_.IsDefault};
if ($defaultOab -ne $null)
{
Write-ExchangeSetupLog -Info ("Existing OAB is Exchange 2010 or older; will create a new OAB");
$createNewOab = $true;
$oabName = $defaultOab.Name + " (Ex2013)";
$oabAddressList = $defaultOab.AddressLists;
$oabGlobalWebDistribution = $defaultOab.GlobalWebDistributionEnabled;
$oabConfiguredAttributes = $defaultOab.ConfiguredAttributes;
}
else
{
Write-ExchangeSetupLog -Info ("Already has an existing Exchange 2013 OAB:" + $e15Oab.Name + "; will not create a new OAB");
}
}
else
{
Write-ExchangeSetupLog -Info ("Existing OAB is Exchange 2013 or newer; will not create a new OAB");
}
}
else
{
Write-ExchangeSetupLog -Info ("Did not find a default OAB; will create one");
$createNewOab = $true;
....
try
{
Write-ExchangeSetupLog -Info ("Creating new default OAB.");
$newOab = New-OfflineAddressBook `
-Name $oabName `
-AddressLists $oabAddressList `
-VirtualDirectories $oabVdirs `
-GlobalWebDistributionEnabled $oabGlobalWebDistribution `
-IsDefault $true `
-DomainController:$RoleDomainController;
}
catch [Microsoft.Exchange.Data.Directory.ADObjectAlreadyExistsException]
{
Write-ExchangeSetupLog -Warning ("Tried to create new default OAB but the object already exists; it may have been created by another instance of setup.");
}
If you encounter the following error message that the default OAB cannot be created during a fresh Exchange 2016 installation.

Why the OAB can not be created?

Some old exchange server information was orphaned in the Active Directory.

Solution

Important: The following steps can damage your running Exchange configuration. Never try to kill all the mentioned keys in a production environment!

1.) Open ADSI Edit and connect with the “Configuration” context.

1

2.) Delete the following tables.

  • “CN=Microsoft Exchange,CN=Services,CN=Configuration,DC=lab,DC=local”
  • “CN=Microsoft Exchange Autodiscover,CN=Services,CN=Configuration,DC=lab,DC=local”

2

3.) Clean up your Active Directory from previous Exchange installations.

  • Delete “Managed Service Accounts”
  • Delete “Microsoft Exchange Security Groups”

3

4.) Delete the created Exchange users accounts.

  • MsExchDiscoveryMailbox.xxxxx
  • Exchange Online-ApplicationAccount
  • FederatedEmail.xxxxx
  • Migration.xxxxx
  • SystemMailbox.xxxxx

4

5.) Now prepare your AD schema again and complete the Exchange installation successful.

 

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