Recently installed a 2013 Exchange server and migrated some mailboxes to it.
What I have noticed is the two mailboxes located on 2013 cannot access each others Shared Calendars or the free/busy data. In the top tab it begins to update then states "No Connection"
When I log into OWA I can see the exchange the above functions just fine.
I have tried re-creating the outlook profile on 2013 and the problem persists. All other functions work and I can view calendars for users on the 2007 Exchange server just fine (vice versa)