diff --git a/stratus1/src/stratus/st_instance.py b/stratus1/src/stratus/st_instance.py
index 983f862b..93affe27 100644
--- a/stratus1/src/stratus/st_instance.py
+++ b/stratus1/src/stratus/st_instance.py
@@ -207,7 +207,8 @@ class Inst :
     if not self._st_cell._hur_cell :
       err = "\n[Stratus ERROR] HurricanePlug : Problem of hurricane cell.\nTry to contact Coriolis team.\n"
       raise Exception ( err )
-      
+     
+    UpdateSession.open()
     inst = Instance.create ( self._st_cell._hur_cell
                            , self._name
                            , self._hur_masterCell
@@ -354,6 +355,8 @@ class Inst :
         err += '               (raw name: <%s>)\n' % str(plug.getMasterNet().getName())
         raise Exception ( err )
 
+    UpdateSession.close()
+
   ##############
   ### Prints ###
   ##############