Odd DNS Resolution Issue

I have been trying to figure a wierd name resolution issue. I have recently setup multiple websites on IIS using host headers due to the server only having one available IP address. I had added each using using a Host (A) record to map each site to the server's IP. After performing the aforementioned actions the site resolves correctly at two office locations; however, the remaining office is unable to access the site.

What is odd is that the name-server at that office has the proper hostname to ip records as well as reverse-dns records. After performing a nslookup the server correctly displays the name resolution for each website. When I try pinging the hostname, it does not respond; however, ping works if I use the server's actual hostname and ip address. It even connects to the default website.

It gets even more bizarre from there; after about a half hour or so, workstations at offices where the resolution does work, would lose their ability resolve the hostname and no longer be able to access the websites. However, when I perform an nslookup they are able to resolve the hostname to ip address correctly.

Can anyone help me with this issue???

Thank you in advance.