internetguide not resolving a domain

Our domain resolves ok using google, opendns and many (all?)other dns servers.
internet guide doesn't seem to be able to resolve our domain. This isn't a dynamic domain - it's static and hosted with a dns service provider in Australia. I've had complaints from a user of our system who thinks we're down because (I believe) he uses internetguide for his dns.

i.e.

 nslookup http://www.oceantracker.net 216.146.35.35 Server: http://resolver1.dyndnsinternetguide.com Address: 216.146.35.35 *** http://resolver1.dyndnsinternetguide.com can't find http://ota1.oceantracker.net: Server failed 

 nslookup http://www.oceantracker.net 208.67.222.222 Server: http://resolver1.opendns.com Address: 208.67.222.222 

 Non-authoritative answer: Name: http://ghs.l.google.com Address: 74.125.71.121 Aliases: http://www.oceantracker.net  ghs.google.com