Asp.net VB Web Service - The Operations times out

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VB

ASP.NET

webservice

I have a web service application project which has to deploy in production server(windows server 2008 r2 standard) and UAT server(web server). One of my web service in the web service application will need to call to a third party web service which named as Service A. I manage to connect to Service A in my UAT successfully but I failed to connect in production server which results in the operation times out. My web service application called the production server failed but I can browse the third party web service in the browser. Both are having the same configuration steps.

Anyone know what might be the cause for this?

Configuration that are done

install .pfx
import .cert (personal & current user)
give permission (IUSR & ASP.NET for web server)

VB Code

Dim cert As New X509Certificate2(HttpContext.Current.ApplicationInstance.Server.MapPath("~/cert/") & ConfigurationManager.AppSettings("CERTIFICATE"), "1234")
ws.ClientCertificates.Add(cert)

Production Error
An error occurred. Error:
System.Net.WebException: The operation has timed out
at System.Web.Services.Protocols.WebClientProtocol.GetWebResponse(WebRequest request)
at System.Web.Services.Protocols.HttpWebClientProtocol.GetWebResponse(WebRequest request)
at System.Web.Services.Protocols.SoapHttpClientProtocol.Invoke(String methodName, Object[] parameters)