This is my scenario:
I have an Exchange\Outlook configuration and secondary calendar that I share out with publishing editor permissions to several co-workers. Works great! They have no problem accessing and editing the calendar. 
I have just added (via sending an invitation and setting permissions for access to publishing editor) 4 more people and oddly they cannot see any of the appointments or add items to the calendar. 
All of us are on exchange via a Microsoft Hosted instance. This is at a University, the staff supporting this are just saying that sharing secondary calendars doesn't work, which I know is not true.
I am in a situation where i will have to find the solution and tell them how to fix it if I can.

Lise Quinn

Are the new members opening it the same way the first ones did?  Secondary calendars can't be opened as a calendar - they need to add the mailbox to the their profile. (They'll only see the folders you gave them permission to see.)