Попробуйте использовать обработчик Application_Error в Global.asax: https://msdn.microsoft.com/en-us/library/24395wz3.aspx
void Application_Error(object sender, EventArgs e)
{
// Code that runs when an unhandled error occurs
// Get the exception object.
Exception exc = Server.GetLastError();
// Handle HTTP errors by sending the JSON (only for Http Error)
if (exc.GetType() == typeof(HttpException))
{
// The Complete Error Handling Example generates
// some errors using URLs with "NoCatch" in them;
// ignore these here to simulate what would happen
// if a global.asax handler were not implemented.
if (exc.Message.Contains("NoCatch") || exc.Message.Contains("maxUrlLength"))
return;
//Return a JSON object
Response.Write(JsonConvert.SerializeObject(new
{
"message": "Parameter missmatch",
"errorCode": "404 (or) something else",
"Status": false
})
);
}
// For other kinds of errors give the user some information
// but stay on the default page
Response.Write("<h2>Global Page Error</h2>\n");
Response.Write(
"<p>" + exc.Message + "</p>\n");
Response.Write("Return to the <a href='Default.aspx'>" +
"Default Page</a>\n");
// Log the exception and notify system operators
ExceptionUtility.LogException(exc, "DefaultPage");
ExceptionUtility.NotifySystemOps(exc);
// Clear the error from the server
Server.ClearError();
}