When users install third-party calendar software, such as Entourage, the installation process may displace iCal as the the default for accepting invitations and other calendar-related functions. This will then prevent iCal from handling these features. While this may be desired for some, other users may wish to revert the calendar functions back to iCal without removing the other calendaring software packages.
Apple Discussions poster reimer1606 writes:
"I bought and installed MS Office 2008 for Mac because OpenOffice was not a solution...However, now Entourage seems to be set as the standard application to handle ics files, although I clicked yes when iCal asked me if I wanted iCal as my standard calendar app. Nevertheless, whenever I receive an ics file in Mail (generated by Thunderbird Lightning extension) and I click on the ics file Entourage opens instead of iCal, as it used to be."
Many applications, including iCal, have options for setting default functions. However, iCal sometimes does not take over all calendar associations when it is set as the default. It seems that the problem lies with iCal not being associated with the ".ics" filetypes. To fix this problem, users should set iCal to open this filetype in the Finder.
Fix: Set iCal to open ".ics" filetypes Locate a calendar file either in a received or sent email iCal invitation, or by opening iCal and exporting a calendar to the desktop. Right-click the calendar and get information on the file. Then under the "Open With" section, select "iCal" from the drop-down menu (or locate the application if it is not in the menu) and then click "Change All..." to associate all calendar filetypes with the iCal program. This should result in iCal being accessed by default when .ics files are opened, either directly by a user or by an application.