This error is due to registry lock enabled which protect any changes . To update Nameserver please disable the registrar lock from clientarea.
Step1: Visit manage domain section of clientarea ( https://www.prabhuhost.com/clientarea.php?action=domains )
Step2: Click on setting icon of domain >manage domain
Click on registar lock disable button and then go to the nameserver section and update the nameservers.
Note : After updating the nameserver please enable Registrar Lock which is for security purpose of domain.
