Cause

There exists a connection of the "Multi-line" representation type in the schematic, whose corresponding connection of the "3D mounting layout" representation type does not exist in the layout space. Thus, the connection between the source and target was not routed in the layout space, or the routing connection between the source and target was deleted subsequently.

Solution

1. Locate the multi-line connection in the schematic using the functionality Go to (graphic) from the popup menu in the Message management dialog.
   
   If the connection has a connection definition point, a jump to it in the schematic is made. If there is no connection definition point, a jump is made to the source of the connection.
2. Follow the connection in the multi-line representation both up to the connected source and the connected target.
3. Highlight the source and target in each case.
4. Use the Go to (counterpiece) functionality from the popup menu to determine whether the source and target exist in the layout space as counterpiece (part placement) of the "3D mounting layout" representation type.
   
5. Locate the respective counterpiece in the layout space from the source and target of the multi-line connection. For this purpose, use the Go to (counterpiece) function from the popup menu.
6. Using the mouse, define in the layout space a selection area that includes the source and target determined.
7. Select the Layout space > Route connections > Route menu items and generate routing connections between the source and target.
8. Then start a new check run.