Norton DNS cannot visit Nitro PDF website.

I can't seem to go to www.nitropdf.com, the website for Nitro PDF on BOTH my Win7 PC and my XP PC.  On my XP PC I got the following message when attempting to go there with IE8:

dns blocked.JPG

 

On the Win7 PC, I simply got a Page cannot be found error when going there with IE9.  Tried all browsers (portable) and none of them can visit that site.  Turning off Norton DNS (reverting back to default DNS) allows me to visit the site.  Please help or fix the problem with Norton DNS