Upgrading SharePoint 2007 Web controls to SharePoint 2010

While upgrading web controls to SharePoint 2010 , we found a issue with Sharepoint Dll in web controls  even  though Sharepoint and related Dlls are present in Assembly directory (C:\Windows\Assembly)

ERROR: Could not load file or assembly ‘Microsoft.SharePoint.ApplicationPages, Version=12.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c’ or one of its dependencies. Access is denied.

Solution: 

You can go to the project properties page (can be accessed from the Project pull down menu), going to the references tab, and adding the path to the  Microsoft.SharePoint dll ( Browse the Dll under the Assembly folder)