Strange Problem

[Ken Holmes]

Hello I am having a strange problem with one domain.
I set it up and it works fine then like 4 days later it stop working under www
www.mynetstore.net
I copy one of my other domains in my named folder and rename the appropriate data and I kill my named server, but it doesn't work right away it takes a while then it works for some strange reason.  Then after 3 or 4 more days it just dies again. Then I have to go back and restore the old copy of the domain I had originally kill the named process and then wait again.  It's getting kinda frustrating.
Here is what my mynetstore.net files looks like.
The strange thing is that the domain that I copy it from works always and never has this problem.

Thanks for any help you can provide.

@               IN      SOA     virtualworldinc.com.    hostmaster.virtualworldinc.com. (
                        1999102101 ; serial
                        3600 ; refresh
                        900 ; retry
                        1209600 ; expire   
                        43200 ; default_ttl
                        )
www             IN      NS      virtualworldinc.com.
www             IN      MX      5       mail.virtualworldinc.com.
@               IN      NS      virtualworldinc.com.
@               IN      MX      5       mail.virtualworldinc.com.