Cause

To address PLC connections you use an addressing scheme in which a certain configuration value is entered under the format element "Counter". You have, for example, selected the "Position (slot / module)" setting. However, In the property dialog of the associated PLC box, a non-numerical value is entered in of the PLC structure data tab in the Position (slot / module) field.

Or the "Channel designation (automatic)" setting was, for example, assigned as a configuration value at the counter. However, a non-numeric value was entered in the property dialog of the associated PLC connection point in the Channel designation field.

Solution

1. In the PLC box or at the PLC connection point enter a purely numeric value in the field, which you also entered for addressing as your chosen configuration value under the format element "Counter".
2. Address the PLC connection points again.