Very strange - my DNS has been up and running fine for years however
recently there have been a few host names I cannot resolve.
for 1. I use the a web dns lookup page on the internet and it finds the
address fine but if I do a nslookup using my own dns server (on nw5.1) it
cannot be resolved. 99% of addresses resolve fine and it's faster if I do
not configure it to forward requests to my ISP's DNS server. Even if I do
however it still cannot be resolved. Though an nslookup using their DNS
server does resolve it.

Can you shed any light on this?