Lync Server 2013 Forest Prep Issue - Task execution failed (Object reference not set to an instance of an object)

Several times while preparing the AD Forest, we run into an issue during the preparation process. This is mostly with a new installation.

You will receive an preparation failed error regardles if you chose the wizard or the Enable-CsAdForest command.
It failes with:

Prepare Forest Active Directory setting exection failed on an unrecoverable error
Command execution failed: Value cannot be null.
Parameter name: InstanceToDelete

This is an wellknow issue in the installation process.

you must use the PowerShell command
Enable-CsAdForest -GroupDomain <AD Domain FQDN> -GroupDomainController <DC FQDN> -GobalCatalog <GC FQDN>


  1. Thanks for the Post !!! It worked and resolved my issue.
    small correction with your powershell: spelling of "Global"

  2. I just stumbled across your Blog a few weeks ago and it has been an invaluable resource. I used this fix for my greenfield Skype for Business 2015 install. Thank you sir.


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