if you have errors in GUI, try powershell enable-csadforest
https://social.technet.microsoft.com/Forums/lync/en-US/827804c1-690b-45c3-93d8-426c66a9a82c/forest-preparation-failed-lync-2013-std-object-reference-not-set-to-an-instance-of-an-object?forum=lyncdeploy