Exchange 2010 DAG , add copy mailbox database error

I got this error after I try to add another database copy to DAG on Exchange 2010

Summary: 1 item(s). 0 succeeded, 1 failed.
Elapsed time: 00:00:02

DB2
Failed

Error:
WMI exception occurred on server 'Servername': The RPC server is unavailable. (Exception from HRESULT: 0x800706BA)

Exchange Management Shell command attempted:
Add-MailboxDatabaseCopy -Identity 'DB2' -MailboxServer 'targetservername' -ActivationPreference '2'

Elapsed Time: 00:00:02

CategoryInfo          : NotSpecified: (0:Int32) [Add-MailboxDatabaseCopy], WmiException
FullyQualifiedErrorId : FD5620B0,Microsoft.Exchange.Management.SystemConfigurationTasks.AddMailboxDatabaseCopy

Any one please help me :(