calendar sharing in exchange

hi.
our organization use exchange 5.5 and we have about 100 users. some of the managers share their calendars so that their secretaries could update/set an appointments for them.
however, in some cases, when i send the calendar to the secretary computer, she gets the calendar, but the calendar stay empty and doesnt get all the appointments that already set up.
i would like to hear some good ideas about it.
thanks a lot.