Users Cannot Remove A Published Calendar

In our Exchange 2010 Organization, we have a calendar in our Public Folders that has been published to Outlook.com (http://calendars.office.microsoft.com/pubcalstorage/.....). We have 20 to 30 users who have not subscribed to this calendar, but the calendar appears in their Outlook 2010 Published Calendars list (File – Account Settings – Published Calendars), and when they launch Outlook, they are prompted for security credentials for the calendar.  We have removed the calendar from the Published Calendars’ list, but within 5 to 10 minutes, the calendar reappears in the users’ Published Calendars list and the next time the user/s launch Outlook. They are prompted for security credentials. All our users have Outlook 2010.

The calendar needs to remain published to the internet, so external personal can access it. We only want to remove it from the internal personal that did not subscribe to it.

Troubleshooting Steps We Have Tried

1. We have tried removing the calendar from Outlook 2010’s File – Account Settings – Published Calendars’ tab. The calendar is not listed on the Internet Calendars tab.
2. We have rebuilt the Outlook profile and the Windows Profile. 
3. We had several users log into freshly imaged machines and when they launched Outlook, they still had the Published Calendar.
4. Launched Outlook with the following switches: /cleansharing, /cleanroamedprefs, & /icalcalendar_name. When the /ical calendar_name switch was ran, it returned “The file {calendar name}.ics is not a valid Internet Calendar file.”
5. For two of the affected users, I opened their user account in adsiedit. I did not find the calendar listed.

Because I could not find the calendar name listed in adsiedit, I am assuming the exchange server holds the Published Calendar subscriptions for a user, but I have not found any articles to verify this. Any additional information or help solving this issue is greatly appreciated.

Thanks!!!!