Asynchronous operations are not allowed in this context. Page starting an asynchronous operation has to have the Async attribute set to true.

I got the following error while running the asp.net web application. It was resolved by adding Async=”true” attribute as instructed by the exception message.

Exception message:

Solution:

<%@ Page Language="C#" AutoEventWireup="true" Async="true" CodeFile="FTPServer.aspx.cs" Inherits="FTPServer" %>

You should register page directive attributes Async=”true” in asp.net page.