Something changed from FreeNAS version 11.2-U8 and 11.3-RELEASE to prevent the joining to an active directory domain. Update 11.3-U1 still has the same issue.
I created two clean installs (in VMs) for FreeNAS 11.2-U8 and 11.3-RELEASE. Version 11.2-U8 joins my active directory domain sucessfully. The same join attempt fails with version 11.3-RELEASE. The error message is included as an attachment.