Some third-party iCal-related utilities, such as Objectpark Software MenuCalendarClock, may prevent you from installing iCal updates that you get from Software Update or download from the Apple site. (“Third-party” refers to products created by companies other than Apple.) When you attempt to update iCal, you receive a message that says that you cannot update iCal because it is “running.” Even if you quit iCal, the issue persists.
What can you do? Check to see if you have a third-party application or utility running that might be accessing iCal resources. Quit or stop the software, then update iCal.
You might also want to contact the developer of the application for possible updates to their software that could avoid this issue.
Important: Information about products not manufactured by Apple is provided for information purposes only, and does not constitute Apple's recommendation or endorsement. Please contact the vendor for additional information.
Important: Mention of third-party websites and products is for informational purposes only and constitutes neither an endorsement nor a recommendation. Apple assumes no responsibility with regard to the selection, performance or use of information or products found at third-party websites. Apple provides this only as a convenience to our users. Apple has not tested the information found on these sites and makes no representations regarding its accuracy or reliability. There are risks inherent in the use of any information or products found on the Internet, and Apple assumes no responsibility in this regard. Please understand that a third-party site is independent from Apple and that Apple has no control over the content on that website.