I was creating a new Xenserver test pool.  A simple thrasher setup that would have two hosts.  I created the pool and when I tried to add the second server; I received an error message:

This server has a different Active Directory configuration to the master

Odd message what has AD have to do with anything? Then….I remembered this was a temporary setup and was added to AD at one point.

I removed it by clicking the “Leave Domain” button found under the Users tab.

It didn’t need a reboot and was added to the new pool.