Issue with access to SOAP service

Hi all,

I stucked with a strange issue. When I start my ASP.NET application locally all works fine. When I deploy it to customer's server a strange error occurs when my application calls web service located on another server. Server does not respond some time and after timeout request fails. Do you have any ideas how to get additional information about this issue? It is clear, that it is because of client server's configuration (where my application run), but how to understand where is a problem exactly?

            ServicePointManager.Expect100Continue = true;
            ServicePointManager.SecurityProtocol = (SecurityProtocolType)_securityProtocol; // == Ssl12 (3072)

            // create a container for an HTTP request
            Logger.Log.Info("Establish: Create WebRequest.");
            HttpWebRequest req = (HttpWebRequest)WebRequest.Create(GetLogInURL());

            // username and password are passed as HTTP headers
            req.Headers.Add("UserName", _userName);
            req.Headers.Add("Password", _password);

            // cookie container has to be added to request in order to 
            // retrieve the cookie from the response. 
            req.CookieContainer = new CookieContainer();

            // make the HTTP call
            Logger.Log.Info("Establish: Get response from CRMOD.");
            // !!! this call below hangs and fails after time out
            HttpWebResponse resp = (HttpWebResponse)req.GetResponse();
            if (resp.StatusCode == HttpStatusCode.OK) 
            {
            ......
            }

Temporarly I have administrative access to client's machine, maybe it will be useful to collect additional information. 

What already did:

• enabled Sl12 on client's server (initially it was not enabled);
• ensured that the problem is not firewall;

Thank you in advance for any idea.