If a ticket is erroneous in nature, you can challenge the ticket and its information in court. Most tickets will identify the process for appeal or court appearance. Have your facts straight, show documentation supporting your argument, and present it clearly to the commissioner or judge. If the officer fails to show or cannot respond well, you will likely win.
How would you know the policeman is writing someone the wrong ticket? Are you that person or is it someone else? In either case if you feel the officer is wrong try not to get into a confrontation with him because you will lose. Go to the precinct where he is stationed and ask for the seargeant in charge
You should contact the police department and let them know that a police officer wrote someone the wrong ticket. Be sure to get the person's driver license's number as this may help the police track this person.