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
Tips on Importing Calendars From Microsoft Entourage to iCal
Note: These steps work for iCal 1.x, iCal 2.x, iCal 3.x and MS Entourage
There are times when importing Microsoft Entourage files in iCal help in scheduling your day activities. For this you need to follow these steps:
1. Launch iCal.
2. Go to the File menu and click on Import.
3. Select ‘Import Entourage Data’
4. Click Import and you are done
Keep in mind that when you import huge files, it takes some time before iCal imports them. You will see a spinning disc cursor which prompts you to wait. Once the files are completely imported, the cursor will change into a pointer. Another thing to remember is that iCal doesn’t import holiday files as they are already included in the package.