Can a Webpage be viewed in a country and not on another ???
I've had this problem with several of my clients who live in Norway. They have a reseller account with us and from time to time, their page is not accessible for 30 to 60 mins. When we check our servers, everything seems to be ok and we are able to see the reseller's webpage. We even had a live chat with our reseller at one point and he was not able to view his page (from Norway) and we were able to view it (from Canada and US).
How is that possible ? The client is not behind firewalls...
Then minutes later, he would be able to view it.
Did you ask him to do them when the problems occur?
Possibly be a corrupt cache. Or if your ISP is using forceful intermediate caching servers (non-optional) for port 80, similar to what NTL are doing in the UK grr... Could be a problem with them. I'm sorry I can't be of more useful help.
Ask him to a do a "telnet resellerdomain.com 80" when problems occur, what does that show?