** Note: The problem and solution discussed below applies for SharePoint 2010 public beta. Future versions may avoid the need to copy this DLL from SharePoint Server. **

One of the cool things about SharePoint Foundation 2010 (the ‘free’ version) is that it supports Business Connectivity Services – which means you can build Business Data Connectivity(BDC) models and deploy to your site.

The Problem

If you have already tried building one (custom .net assembly), you will encounter the following error:

Failed to load receiver assembly "Microsoft.Office.SharePoint.ClientExtensions, Version=14.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c"

The Solution

The solution is very simple – If you have SharePoint Server 2010 beta installed, copy the Microsoft.Office.SharePoint.ClientExtensions.dll from C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\ISAPI to the following locations where SharePoint Foundation 2010 is installed:

1) GAC

2) C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\ISAPI

Now,  deploying your BDC model (custom .net assembly) from visual studio should work :)