Are you using VTScada Alarm Notifications while running VTScada as a Windows Service? The ability to run VTScada as a service was introduced in version 11.1. It allows an application to optionally run in the background without an active user interface.
Please note that Microsoft does not permit Windows services to access SAPI, the built-in Windows text-to-speech engine. This means that if you're using the VTScada Alarm Notification System and you have configured your application to run as a service, the outgoing alarm calls will be silent.
This is not an issue for standard VTScada installations or if you are using the IVONA speech engine (not available to new users). Otherwise, we recommend the web-based Twilio® platform for alarm annunciation (supported in version 11.3 and higher).