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.