Orphaned structure member system end port.
Every member system has two end ports related to it (the end port at the start of the member system and the end port at the end of the member system). When the member system was deleted, one of the end ports was not deleted along with the member system.
Deleting a member system failed to propagate the delete operation to one or more of its end ports.
What You Should Do
Run the delivered custom command to remove the offending port.
Ask your database administrator to back up the model.
Supply all information possible that might have led to this situation, and submit this information along with the backup to Hexagon PPM Support.
Execute the Clean Database custom command to remove the port.