AX 2012 - Enterprise Portal - Adding a new column to activities page. SysListPageContentArea cannot be edited in VS2010. Namespace AxModeledActionPaneControl doesn't exist.

Trying to add a new column on Home\Sales\Activities. 

I found that this Webpart is 'SysListPageContentArea'. It is located under AOT->Web->Web Files->Web Controls:

Now trying to edit it in Visual Studio 2010. At the compilation it returns the error: 

" 

Error 1 The type or namespace name 'AxModeledActionPaneControl' does not exist in the namespace 'Microsoft.Dynamics.Framework.Portal.UI.WebControls .WebParts' (are you missing an assembly reference?) c:\users\apascari\documents\visual studio 2010\Projects\EPWebApplication4\EPWebApplication4\ SysListPageContentArea.ascx.designer.cs 84 83 EPWebApplication4 

" 

Where I can find the last version of 'Microsoft.Dynamics.Framework.Portal.dll' to have namespace 'AxModeledActionPaneControl' ?