Cause

You have created the same terminal (with the same DT and designation) more than once in the terminal strip navigator, or placed the same terminal in the schematic even though multiple entries with the same DT and designation are not permitted.

Solution

Possibility 1

Double-click the terminal that has been used more than once in the terminal strip navigator or in the schematic, and bring the Terminal tab to the front in the Properties <...> dialog. In the Properties group box, check the status of the Allow same designations check box. Activate the check box if you want to create or place the terminal with the same DT and designation more than once.

Possibility 2

Double-click the terminal that has been used more than once in the terminal strip navigator or in the schematic, and enter a new terminal designation in the Properties <...> dialog.

Then start a new check run.