After upgrading to MVC 4 async tasks don't work

Question

I've upgraded my website to MVC 4 from MVC 3 and started experience this error:

An asynchronous operation cannot be started at this time. Asynchronous operations may only be started within an asynchronous handler or module or during certain events in the Page lifecycle. If this exception occurred while executing a Page, ensure that the Page is marked <%@ Page Async="true" %>

Though it worked in MVC 3.

This code:

            Uri uri = new Uri(string.Format(
            UrlTemplate,
            ServiceId,
            HttpUtility.UrlEncode(id),
            HttpUtility.UrlEncode(org),
            HttpUtility.UrlEncode(user),
            HttpUtility.UrlEncode(activity),
            HttpUtility.UrlEncode(module)));

        using (var client = new WebClient())
        {
            client.DownloadDataTaskAsync(uri);
        }

So, did you mark your pages with Async=true, and did it work then? — Roy Dictus
– Roy Dictus, Commented Nov 19, 2012 at 9:31
No, I didn't mark them. It wasn't neccesary for MVC 3. How can I do it? — Sergey
– Sergey, Commented Nov 19, 2012 at 9:34
Maybe the problem is with the .NET Framework 4.5. Because at the previous time (with MVC 3) I didn't experience any of these problems — Sergey
– Sergey, Commented Nov 19, 2012 at 9:42
As the error message says: ensure that the Page is marked <%@ Page Async="true" %>. This is a feature new to MVC 4. — Roy Dictus
– Roy Dictus, Commented Nov 19, 2012 at 9:52

Roy Dictus · Accepted Answer · 2012-11-19 10:07:09Z

2

As the error message says: ensure that the Page is marked <%@ Page Async="true" %>. This is a feature new to MVC 4.

answered Nov 19, 2012 at 10:07

Roy Dictus

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