Cause

A CPU name for which no CPU could be found in the project was stored at a PLC box.

This check run only checks PLC boxes that are main functions.

Solution

1. Locate the PLC box 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. Enter the name that was stored at the associated CPU of the configuration project in the CPU: Name [1] field.
5. Click [OK].
6. Then start a new check run.