You can find how to here:Aug 17, 2012 · Choose Reset Sync Services. Click Reset Sync History. Test for the ... Resetting SyncServices resets your Mac OS X User Account's Sync settings and …
Be sure you have quit all Office applications including Entourage and Outlook. If that doesn't solve the problem:
Open Activity Monitor in the Utilities folder. Select All Processes from the Processes dropdown menu. Locate the process, select it, click on the Quit icon in the toolbar then click on the Force Quit button.