New Post: Unable to open Exchange 2010 users mailbox from exchange 2013's user mailbox from MFCAMPI. And vice-versa

1. Created two super users(1 on exchange 2010 and other on exchange 13 in same organisation)
2. Assigned all necessary permission to these both users in AD.
   Get-MailboxDatabase | Add-ADPermission -user Domain\User -AccessRights GenericAll -InheritanceType All
   

Get-MailboxDatabase -includepreExchange2013 | Add-ADPermission -user Domain\User -AccessRights GenericAll -InheritanceType All

1. When I open MFCAMPI from exchange user mailbox, and try to open any exchange 2010 user's mbx, then get following error
   

Error:
Code: MAPI_E_FAILONEPROVIDER == 0x8004011D
Function OpenOtherUsersMailboxFromGal( lpMAPISession, lpAddrBook, &lpMailboxMDB)
File MainDlg.cpp
Line 729

*Interestingly, from outlook of exchange10/13 user, I can open mailbox of exchange13/10 user mailbox. but failing from MFCMAPI only.
*From exchange 2010 super user via MFCMAPI, I can open any exchange 2010 mbx.
*From exchange 2013 super user via MFCMAPI, I can open any exchange 2013 mbx.
__*But, when I go for cross, it fails.__