User A is a delegate who has calendar access to user B's mailbox. User A and User B are in different domains. User A lost access after User B's mailbox was moved from Exchange 2003 to 2010. User A can still access Exchange 2003 and 2010 calendars within the same domain, but cannot access Exchange 2010 calendars in another domain (User A is on Exchange 2010). The calendar entries show as "Busy" or "Tentative". Tried reapplying the permissions, but no luck. Anyone know to fix this? Thanks.

I actually reapplied the permissions again and seems to be working now.