[RESOLVED] Application working on one computer but not another

Has this ever happened to anyone? It has happened to me and one of my customers in the past but I have no idea how he diagnosed it and it is happening with another one of my clients now. The application runs, but the HTTP requests do not. The application works 100% perfect on my own computer but not the customers. He has both the 1.1 and the 3.5 framework installed, and uses Vista (same as me).

Can anyone shed some light on this situation because this is a huge huge huge problem that I would rather not have to worry about in the future with other clients. ANY help is greatly appreciated. Thank you in advance.

Windows firewall blocking the app from accessing the Internet?

Just completely disabled the firewall and still the same result. :(

Try to telnet from the client's machine using the same port and IP address. Does your client use proxy?

My client is not using a proxy, but the application does support proxies. I nor my client know the first thing about telnet though so if possible could you explain a bit more? As I said everything works fine on my end. I just tested it on my laptop as well and it's all good on there as well. Super super frustrating.

Ahhhhhhhhhhhhhhhh, nevermind. We got it figured out. He had a system proxy set and once he disabled it everything was all good. Sorry about that. Thanks for the quick help too. Very much appreciated.

From the command prompt:
>telnet {ip address} 80

i.e.
telnet 127.0.0.1 80

If the connection was established there will be a response something like:
HTTP/1.1 400 Bad Request

if not - there will be an error.