Hi Elizabeth,
Do you have a iPod or iPhone connected to the Mac through a USB hub?
Are there any 3rd-party plug-ins or add-ons installed?
This article: from
http://support.apple.com/kb/TA22611 provides more information about 3rd-party plug-ins.
Mac:
+/Users/username/Library/iTunes/iTunes Plug-ins+
+/Library/iTunes/iTunes Plug-ins+
If the issue is not caused by a 3rd-party plug-ins, try removing and reinstalling iTunes as shown here:
http://support.apple.com/kb/HT1224
Message was edited by: Jason L