A 3D Reference object has no parent in the hierarchy.
A 3D reference object that has no relationship to a 3D reference parent object has been found in the database. This message will be displayed for any of three situations:
An R3DRoot object does not have a ReferenceHierarchy relationship to a folder parent object.
An R3DProject object does not have an R3DHierarchy relationship with a parent R3DRoot object.
An R3DAttachFile object does not have an R3DHierarchy relationship with a parent R3DProject object.
These are unexpected errors with no known causes.
The hierarchy of 3D References will not be displayed correctly in the references tab of the workspace explorer.
What You Should Do
A repair command is provided for the two cases where the child object is an R3DRoot or an R3DProject object:
Open the model.
Click Tools > Custom Commands.
Run the Clean Database custom command.
On the Clean Database dialog box select the object displayed with the message identified above.
Click Clean Now. This operation will create a new relationship between the R3DRoot object and an orphan R3DProject object, or between a parent folder object and an orphan R3DRoot object.
Close the Clean Database dialog box.
Save and Exit the session.
It is impossible for the repair command to know which available R3DProject, if any, is appropriate as a parent object for an orphan R3DAttachFile object, so no automatic repair action can be provided. You will have to correct the problem manually.