Excellent help MadisonP.

Greetings Dinger,

As you tested in a new user we know this is not an issue with iCal, rather with some piece of data in your user account. Good testing!

1. Backup your data: http://support.apple.com/kb/HT1553

2. Remove the following to the trash and restart your computer:

Home > Library > Caches > com.apple.ical

Home > Library > Calendars > Calendar Cache, Cache, Cache 1, 2, 3, etc. (Do not remove Sync Cache or Theme Cache if present)

Home > Library > Preferences > com.apple.ical (There may be more than one of these. Remove them all.)

—NOTE: Removing these files may remove any shared (CalDAV) calendars you may have access to. You will have to re-add those calendars to iCal > Preferences > Accounts.

—NOTE: To get to “Home > Library” in Lion hold down the option key and click on “Go” while in the Finder.

3. If the issue persists boot into Safe Mode and test again and report your results: http://support.apple.com/kb/HT1455

Hope that helps.

via iCal keeps crashing when opened in OS…: Apple Support Communities.