Cause

You have copied an item that can be changed in length (such as a mounting rail or a wire duct) in the layout space and have left the DT unchanged after pasting. Or you have renamed such an item in the layout space and in the process have used a DT that is already being used.

Solution

1. Locate the item existing several times in the layout space by using the Go to (graphic) function from the popup menu in the Message management dialog.
2. Assign a unique displayed DT in the property dialog.
3. Then start a new check run.