Backup Exec 2010 can not view DAG, Exchange 2010

Some people are currently faced with the following problem :

You are unable to access my Exchange 2010 DAG from Backup Exec 2010 for backup.
The DAG is visible from the selection list but fails authentication.

There are many people who as this quetsion on the net, but no expert from any forum the anwser yet.
The Backup Exec server has a Windows Server 2008 R2 OS and has the Exchange Management Tools installed.

My backup guy was fighting with this problem a few days and then finally asked my opinion.
After looking around the setup for a few minutes I found the problem and fixed it within seconds !

The solution is simple actually.
When you are faced with such a problem make sure that your DAG Cluster it’s OK and does not have any failed state.

Please check your DAG Cluster via the “Failover Cluster Management” in control panel.
I bet your DAG has the Cluster name / IP address in the Failed state.

Bring that resource up and everything should be ok.