Avast Endpoint Protection Suite. Clients unable to update defs

We have been using the Avast Free for Edu product for years. Our district was one of the first to use this product. We have now ran into a problem where clients are unable to update defs for the server. The error is, “Cannot connect to 172.16.1.20:16135 {unknown 16135}”
I checked the mirror ports which are set correctly but now the server is refusing connections. Any help would be appreciated.