Edit: After half day, my wife’s Mac started having the same problem. I have then applied the solution that I found in the Apple
Share iCal with your Family
If you have a lot of work-related tasks and want your family to be aware of them, you can share your calendar with them using either the MobileMe Internet service or a private server.
1. iCal offers two default calendars – Home and Work. Select the Work calendar (or whatever you use) and then choose Publish from the Calendar menu.
2. In the window that appears, enter the name of the calendar (if you want it to be other than Work or the name you chose), select where to publish it (MobileMe or a private server), and choose your preferable publishing parameters.
3. When ready, click Publish. Now you can share the URLs where your calendar has been published.