Calendar Sharing not available error message

Trying to share my calendar with staff at the office here. I get the error:

Calendar sharing is not available with the following entries because of permission settings on your network.

I am using Offiice 2007 SP1, Exchange Server 2007 SP1

I can however go to the other workstation and use the "open a shared calendar" option to access my shared calendar.

It does work on some accounts, but not the majority of accounts.

Where do I start trouble shooting this issue? How do I check the "permission settings on my network"

Sorry if this is an easy one, I'm a new user to exchange. This is not a full production setup yet, still testing before I let folks know what it can do.

Thanks

Kevin Maracle

First Nations Technical Institute