To inform users a defect was encountered involving Modbus Messaging (Access Control service) communication.
Unity Pro v4.0
The defect manifests when the Modbus messaging service is not used and access control box under the Messaging tab is not checked but the access control table is configured (there is some lines defined on it). This configuration will disable I/O Scanning and Global Data services.
Customers can resolve this issue in one of two ways:
1) Upgrade to Unity 4.1. It prevents users to fill in any data in the access control table without checking the Access Control box.
2) If using Unity 4.0, do not configure the access control table if you do not plan to restrict module communication. If you want to use the Access Control feature, ensure that you check the Access Control box.