Fixing bug 160378.

calendar/locales/en-US/chrome/calendar/calendar.dtd

@@ -95,6 +95,7 @@
 <!ENTITY newevent.recurrence.tab.label "Recurrence" >
 <!ENTITY newevent.contacts.tab.label "Contacts" >
 <!ENTITY newevent.files.tab.label "Files" >
+<!ENTITY newevent.cancelled.label      "Cancelled" >
 
 <!ENTITY newtodo.completed.label "Completed">
 <!ENTITY newtodo.duedate.label "Due Date">