Ok, so I was trying to setup a DAG on my Exchange 2010 SP3 which was installed on Windows 2012, I could create the DAG without any issue and also I was successful in assigning it an IP address but when I tried to add my two DAG members I kept getting an error.
The File Share Witness that I used was a 2012 member server and not an Exchange Hub transport so I double-checked that if it was added in the "Exchange Trusted Sub-System" group in AD and also the "Exchange Trusted Sub-System" was added in the local admin group on the server.
After a lot of looking around I found out that you have to Pre-Stage the CNO (Cluster Node Object) in Active Directory due to the Windows 2012 permission change and only then go ahead and create the DAG!
- So I deleted the DAG from the Exchange 2010 EMC
- In Active Directory User and Computers I created a new computer account called "DAG" and after creation I right clicked the object and selected "Disable"
- I then added the "Exchange Truster Sub-System" group under the security permissions on the computer account I created and gave it full-control...alternatively if you don't want to add the "Exchange Trusted Sub-System" group on the DAG computer account you can also add the individual node computer accounts and assign them full control as well and it will work.
- After this I created the DAG using the EMC and assigned it a IP address and this time when i tried adding the 2 DAG members I was successful!
Hope it helps!