Cause

The source or the target of a connection of which there are several representation types in the project is not available in the representation type. For example, the target of a routing connection of the type "3D mounting layout" that exists as a multi-line connection in the schematic has been deleted in the layout space.

Solution

Possibility 1

1. Locate the connection in the schematic by using the Go to (graphic) functionality from the popup menu in the Message management dialog.
2. Search the missing source or the missing target via the existing connection.
3. Place the missing source or the missing target.

Possibility 2

1. To remove data from your project that is not required anymore, select the following commands: File > Extras > Command group Organize > Project > Command group Optimize > Compress project.
2. In the compression settings activate the check box Remove unplaced connections.

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If required, start a new check run.