Intermittent failures for co.uk requires DNS server to be restarted

A client has reported a problem with co.uk domains every few weeks. We're in the US but they need to access co.uk sites often and every now and then it's not working. I try to PING from the RD server and see that the PING request isn't able to resolve the name and gives me an error "PING request could not find google.co.uk. Please check the name and try again."

This is the same result if I PING ebay.co.uk or bbc.co.uk for two more examples. When I use NSLookup from the RD server directly I get similar results. When I look up google.co.uk I get an error saying that it's a non-existent domain. When I look up google.com it resolves it correctly. When I look up ebay.co.uk and bbc.co.uk it fails again.

Resolution from the RD machine works fine when I query an external DNS server, for example, Google's public DNS servers. It's just when trying to resolve IPs of co.uk domains from machines on the LAN from the Domain Controller itself.

There is only one DNS server on this network with about 15 client machines. The server is running Windows 2003 R2. The fix so far is to restart the DNS service. It takes a while for the problem to present itself again and I only hear about it within a few weeks when the client reports this problem again.

I'm really not sure which way to go with it at this point beyond reacting to the client's complaint every few weeks.