Convertion of proprietorship into partnership under kvat

i have one client who is running his business since 30 to 40 year which he aquired from his father as parter , right now he is running the same business as proprietorship , but he wants add his son as partnership whether it is possible , but in vat official are telling close the old firm & take fresh registration as partnership , i am required clarifiaction why we have to close the old firm , we are intending coversion of proprietorship into partnership.