System.Data.DataSetExtensions Build Error

Today I opened a Web Application (developed by someone else) from a client and tried to build it in Visual Studio 2008 and I got this build error:

Could not load file or assembly 'System.Data.DataSetExtensions, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' or one of its dependencies. The system cannot find the file specified.

Upon further investigation I figured out that the Framework 3.5 has changed the System.Data.DataSetExtensions from version 2.0.0.0 to 3.5.0.0. To resolve the problem,

1. Right-Click on the Web project and select "Property pages", The following window will load up and we can clearly see in the following screenshot that the System.Data.DataSetExtensions assembly is of the version 2.0.0.0.

2. Highlight the v2.0.0.0.0 assembly and re-add the same assembly using the Add button. The Property pages should now look as follows:

3. That's it you are done, atleast with this error....