Hi Guys I have setup a webserver which is accessible to the web via my line's IP address. The problem is I have purchased a domain and whenever I try to set the nameservers with my IP address the system rejects it. Why is this so ? and how can I fix it ?

did you setup your nameservers on your own pc (ip)? Your ns/dns needs to be setup before you update your domain registar or it will return as unvaild.

How do I do that ?

Are you on a cPanel server ? What is the exact error message that you are getting?