Cause

You are using a cross-section / diameter that does not correspond to the project template. Cross-sections or diameters that can be assigned to all connections of the project can be specified in the dialog Settings: Cross-sections / diameters (command path: File > Settings > Projects > "Project name" > Connections > Cross-sections / diameters).

The value selected by you is not contained in the template table.

Solution

Possibility 1

Select a value that is contained in the Cross-sections / diameters template table.

1. To do this, open the Properties <...> dialog for the corresponding connection or the corresponding connection definition point.
2. Click [...] next to the Cross-section / Diameter field.
3. Select one of the predefined color codes or color names in the Cross-sections / diameters dialog that opens and click [OK].

Possibility 2

Extend the Cross-sections / diameters template table with the value that you want to use project-wide.

1. Select the following commands: File > Settings > Projects > "Project name" > Connections > Cross-sections / diameters.
2. In the Settings: Cross-sections / diameters dialog, click (New) and enter the desired value in the new table row.
3. Subsequently click [OK].

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If required, start a new check run.