Sounds like a permissions issue.
I would start with one particular user on one machine.
Check the permissions of the machine and the user to make sure they have the rights needed to get to the public folder.
first question is, when trying to access it from the second pc are you using the same account that created it? if not, login as that account to see if you can. if you can then with that account right click the calendar, go to properties, then permissions. default should be REVIEWER if you want everyone to see it but not be able to edit it. if that works but you want them to have more than view go to the following link for more info on each permission:
Outlook folder permissions.