Cause

The same CPU name is used more than once within the same configuration project and the same workstation.

Solution

1. Locate the PLC box of the CPU in the schematic using the Go to (graphic) functionality that is provided by the popup menu of the Message management dialog.
2. Open the property dialog of the PLC box.
3. Bring the PLC structure data tab to the front.
4. In the properties list, change the value of the CPU: Name [1] field.
5. Click [OK].
6. Then start a new check run.