DAG in Exchange 2010 is not working properly

Dear Experts,

i have following environment:

AD main Site:
2 x CAS/Hub Servers (with 1st server as file share witness)
2 x Mailbox Servers

AD DR Site:
1 x CAS Server
1 x Mailbox Server

My mailbox servers are in DAG across AD Sites, something has gone wrong and i cannot open properties of my DAG, it gives this error:

A server side administrative operation has failed, Operation failed with message:  Error 0x721 (A Security package specific error occurred) from Cli_GetDagNetworkConfig.

Please see attached complete error:
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MCIT-LibyaAuthor Commented:

The problem turned out that on one of the network card of DR Site, IP of main site was given and that was creating problems. I disabled that network card but didn't helped, I just remove that IP and it start working fine.

Thanks all for your kind help.
MAS (MVE)EE Solution GuideCommented:
Please run “DCDiag /v /a” and “NetDiag /v” to check the health of DC and connection to DC from Exchange server.
Check the status in the “Failover Cluster ” console
What about the IP of the DAG?

Please check your AD health as well
MCIT-LibyaAuthor Commented:
Dear MAS,

DCDiag seems OK, NetDiag didn't work because i have windows server 2008 R2 as DC.

in failover cluster it is showing DR Server as offline and also it's cluster network is offline.
when i try to run the cluster service on DR it give RPC Server not available.

i have 2 dag ip's, one of main Site subnet and other for DR Site subnet.

it doesn't seems like AD Issue, it seems some network configurations issue with failover cluster or DAG.

Please advise.
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MAS (MVE)EE Solution GuideCommented:
Can you create new DAG?

Just to be sure about ur AD health
MCIT-LibyaAuthor Commented:
Yes i can create new DAG.
on failover cluster i have attached error
MCIT-LibyaAuthor Commented:
I did following things:

remove 2nd IP of DAG from Failover Cluster
Shutdown Cluster from Failover Cluster and start it again.

now DAG properties are working fine ( i had to do it on all servers)

still my DR Server is showing as offline.
i planned to remove the DR mailbox server from the DAG and add it again as it is not hosting any database.

from main site, when i try to remove server it gives error that one of the database copy is in DR Site so i cannot remove that server from DAG whereas it is not true.

how can i forcefully tell exchange that database copy does not exist anymore, or how can i forcefully remove my server from the DAG to add it again?
MCIT-LibyaAuthor Commented:
i got attached error when i open Database managment tab
Miguel Angel Perez MuñozCommented:
Can you check AD consistency? It is possible some machine accounts (focus on DAG and Exchange servers accounts) are updated on one site but not on the other side. You can use Sync-ADObject to force replication of one object to the rest of domain controllers.

Then, you can remove database (moving mailboxes first to another) using remove-mailboxdatabase or deleting using adsiedit if cmdlet not works: https://penguyen.wordpress.com/2013/08/01/force-removing-exchange-2010-database-adsiedit-msc/
MCIT-LibyaAuthor Commented:
Main Site and DR Site were in different IP Subnets and DAG has 2 IP's for each site.

by mistake on one of the network card of DR Site IP address from main site subnet was given, I removed that and all start working fine.
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