Cause

A planning object occurs more than once in the project with the same designation.

Solution

1. Locate the planning object that occurs multiple times using the Go to (graphic) and Go to 2nd coordinate or Synchronize selection functions from the popup menu of the Message management dialog.
2. Call up the Properties <...> dialog of the planning object and bring the <Planning object - displayed name> tab to the front.
3. In the Designation field, change the character string, so that a unique planning object is stored in the project.
4. Click [OK] to close the Property dialog, then start a new project check.