DNS problems on Linux dedicated server

I have a DNS problem on my server which my host cannot seem to fix. I use custom nameservers: [login to view URL], [login to view URL] The server runs CentOS with Apache and BIND. The problem is: when using certain ISP's nameservers, my domains are inaccessible (I get "Looking..." in the browser and "Page cannot be displayed"), however I can access the server at: [login to view URL] For example, a few sites such as: [login to view URL], [login to view URL], [login to view URL] are inaccessible with various hosts in the UK. The problem nameservers are: [login to view URL], [login to view URL] I have had reports that a lot of other U.K. based nameservers don't work either. I have also tried: 4.2.2.2, 4.2.2.1 (which works sometimes) The server was working fine until I recently had an upgrade from Linux kernel 2.4 or 2.6. Can anyone diagnose or help? Thanks