DNS Lookp Error

Currenly i am using Kerio Winroute as Firewall on win 2003 server, with 2 NIC. Before some days i have change my isp and now it’s giving blow error when browsing any http page after reloading page 1 or 2 times it will work.

In my local system i have configured as below

Gateway :- 192.168.52.2 (my Firewall IP)
DNS : 1) 202.138.96.47 (DNS of ISP)
2) 202.138.103.100 (DNS of ISP)

When i do Nslookup it give below error some time

Server : murnsc001.rillinfo.net
Address: 202.138.96.47

DNS Request timed out.
time out was 2 secounds.
***Request to murnsc001.rillinfo.net time-out

Can any one help me??????????