diff --git a/addons/base_calendar/base_calendar.py b/addons/base_calendar/base_calendar.py
index 5bc12c69671..f7a67adae11 100644
--- a/addons/base_calendar/base_calendar.py
+++ b/addons/base_calendar/base_calendar.py
@@ -1416,6 +1416,16 @@ e.g.: Every other month on the last Sunday of the month for 10 occurrences:\
         @param context: A standard dictionary for contextual values
         @return: True
         """        
+        #removing useless value
+        if type(ids) == int or (type(ids) == list and len(ids) > 0):
+            old_vals = self.read(cr, uid, ids[0] if type(ids) == list else ids, ['rrule'], context)
+            if not old_vals:
+                old_vals = {}
+            if not 'rrule' in old_vals:
+                old_vals["rrule"] = ""
+            if 'rrule' in vals and not vals['rrule'] and not old_vals['rrule']: 
+                del vals['rrule']
+        
         if context is None:
             context = {}
         if isinstance(ids, (str, int, long)):
diff --git a/addons/users_ldap/__openerp__.py b/addons/users_ldap/__openerp__.py
index 7d54e1fc95e..9559c0f5d31 100644
--- a/addons/users_ldap/__openerp__.py
+++ b/addons/users_ldap/__openerp__.py
@@ -40,7 +40,7 @@ This module only works with Unix/Linux
     "active": False,
     "installable": True,
     "certificate" : "001141446349334700221",
-    "dependencies" : {
+    "external_dependencies" : {
         'python' : ['ldap'],
     }
 }