This alert is sent when a certificate is revoked and can no longer be used. This could prevent the communication between internal system components and with external systems completely.
The certificate has to be renewed or replaced with a valid certificate. The system uses certificates at various places for internal communication (server certificate), encryption and signing, web application, etc.
If the problem remains, please contact the support service and send the log files of the related service(s).
Log files are available under "APPLICATION_FOLDER\log" (by default C:\Program Files\Verba\log) folder on each server.