fix error

app/models/bulletin.rb

@@ -68,7 +68,9 @@ class Bulletin
 
   before_create :set_expire
   before_save :check_limit
-  
+  def to_calendar_param
+    self.to_param
+  end
   def calendar_type
     CalendarType.where(:category_id.in => self.calendar_type_id)
   end