I installed Outlook 2007 for our users using an MSP file created with the Office Customization Tool, where under User Settings, Account Settings, Internet Calendar Subsciptions, Do not include Internet Calendar integration in Outlook was enabled. I found that I cannot open a single appointment ICS file because of this (error message: "system administrator has turned off this feature").
I cannot find a setting in Outlook, Outlook setup, nor even registry settings, to change this back to enable Internet Calendars. I could go with a complete reinstall, but that seems excessive. How do I re-enable use of iCal in Outlook?