'Microsoft.Owin.IOwinContext' does not contain a definition for 'GetUserManager' and no extension method?

The following code is copied from the Asp.Net Identity 2.0 sample.

private ApplicationUserManager _userManager;
public ApplicationUserManager UserManager
{
get
{
return // Error
_userManager ?? HttpContext.GetOwinContext().GetUserManager<ApplicationUserManager>();
}
private set
{
_userManager = value;
}
}

However it gets the following error?

> Error 3 'Microsoft.Owin.IOwinContext' does not contain a definition for 'GetUserManager' and no extension method 'GetUserManager' accepting a first argument of type 'Microsoft.Owin.IOwinContext' could be found (are you missing a using directive or an assembly reference?)

**Update:**

The version 2 of Microsoft.AspNet.Identity.Owin.dll already exists in ...\packages\Microsoft.AspNet.Identity.Owin.2.0.1\lib\net45.

However, the view definition of `HttpContext.GetOwinContext()` are different between my project and the sample. The first three lines of my project are

<pre>
#region Assembly Microsoft.Owin.Host.SystemWeb.dll, v2.0.0.0
// C:\......\packages\Microsoft.Owin.Host.SystemWeb.2.0.0\lib\net45\Microsoft.Owin.Host.SystemWeb.dll
#endregion
</pre>

while the sample is

<pre>
#region Assembly Microsoft.Owin.Host.SystemWeb.dll, v2.1.0.0
// C:\....\sample\packages\Microsoft.Owin.Host.SystemWeb.2.1.0\lib\net45\Microsoft.Owin.Host.SystemWeb.dll
#endregion
</pre>

But I already updated all Owin Nuget packages to the newest version using Neget.

The extension method was moved to a different namespace, try adding

using Microsoft.AspNet.Identity.Owin;