We have three 5520s on the 3rd floor and 2 on the 2nd. These are connected with a 2 fiber trunk. In the last 2 months we have had 1130s on the 3rd floor failing to communicate with the server on the 2nd floor. All the units on the 3rd floor have blinking green base lights. Resetting all units by power cycling causes the stack to reform and to work for a period of time. This is the 3rd failure in 2 months--has worked fine for several years. My best guess in that the base unit has intermitten failures. Any one with other thoughts.