No response from webclient or httpWebResponse

I've come accross a very unusual problem that I'm trying to find a work around to.

I have an application that connects to a mysql db through php scripts. Content is filtered back to the app via XML and then displayed on the forms for the users.

Now on some of my beta testers computers they are getting timeout errors when using the application. It's only a handfull of people but I like to develop apps that work 100% for all or not at all.

They all have this in common. They are hosted by an ISP that shares an IP address within a Postal/Zip area. and also I have a problem with my testbed at work which has 2 internet facing IP addresses which are load balanced.

I've put my development machine on this network and stepped through the program. It sends requests out the the site no problem which are recieved and dealt with accordingly.

But which ever method I use, I don't get a response.

Dim rs As WebResponse = req.GetResponse()

times out and

result = System.Text.Encoding.ASCII.GetString(myWebClient.U ploadData(URL, GetFunction, System.Text.Encoding.ASCII.GetBytes(DataString)))

Produces same response which is a connection timed out error and in some cases the remote connection was closed.

to me it's as if the initial query is recieved, but then the website doesn't know where to send the response as there might be 10 or more computers on the same ip, or in my case, the firewalls have switched me to the other IP address.

But this is crazy as I'm able to view websites from the same site on the same computer.

Has anyone else seen this before or know of any way to get around it?