How to process WebResponse when .NET throws WebException ((400) Bad Request)?

Using a try/catch block like this and processing the error message appropriately should work fine:

    var request = (HttpWebRequest)WebRequest.Create(address);    try {        using (var response = request.GetResponse() as HttpWebResponse) {            if (request.HaveResponse && response != null) {                using (var reader = new StreamReader(response.GetResponseStream())) {                    string result = reader.ReadToEnd();                }            }        }    }    catch (WebException wex) {        if (wex.Response != null) {            using (var errorResponse = (HttpWebResponse)wex.Response) {                using (var reader = new StreamReader(errorResponse.GetResponseStream())) {                    string error = reader.ReadToEnd();                    //TODO: use JSON.net to parse this string and look at the error message                }            }        }    }}

However, using the Facebook C# SDK makes this all really easy so that you don't have to process this yourself.

The WebException still has the "real" response in the Response property (assuming there was a response at all) so you can get the data from that within the catch block.