How to disable WebRequest WebResponse Javascript error prompt?

Hi!
i'm working on google map. when i send a request using 'request.GetRequestStream();' sometime(when net goes down) it show javascript error. i want to disable this error prompt and show my custom error. Please help me.....



try
{

WebRequest request = WebRequest.Create(sURL);
            request.Timeout = 10000;
            // Set the Method property of the request to POST.
            request.Method = "POST";
            // Create POST data and convert it to a byte array.
            str ...