Cache notifications are not supported because the named cache has been created without notifications enabled.
Assembly: Microsoft.ApplicationServer.Caching.Core (in Microsoft.ApplicationServer.Caching.Core.dll)
In order for your application to use notifications, you need to enable them on a named cache. Use the NotificationsEnabled parameter with the New-Cache or Set-CacheConfig commands. For more information, see Cache Administration with PowerShell (Velocity).