Recently I had to install Exchange 2010 on Windows Server 2012. This was great until I tried to add mailbox servers to the DAG, only to get a bunch of obscure error messages that didn’t mean anything!
It would appear that from Windows Server 2012 it can no longer create the cluster account correctly. When you create a DAG nothing actually happens to form the cluster, instead it is just an object inside Exchange. The cluster objects including the computer account for the cluster get created when you add the first mailbox server to the DAG. The first time you try and add the first member it seems to mostly work then error out, later retries result in an obscure error message.
It would appear the way to resolve this is to pre-create the cluster computer account, and add Exchange Trusted Subsystem with full control on the account. It appears the code to create the cluster computer account within Exchange is totally broken when it comes to Exchange 2010 with no fix other than delete and pre-stage. I set all kinds of permissions and none made a difference!