error BC32206: Indirect reference is being made to assembly System.Web.Extensions version 3.5.0.0

I have downloaded a .NET Framework solution from Team System Source Control on a new computer and tried to rebuild the solution.
The solution contains 14 projects, a web site project, libraries, user control projects, console application projects, etc.
One of the projects included in this solution is the AjaxControlToolkit which I had made some updates or modifications on the code of the Ajax Control Toolkit source codes.
Because I had updated the codes, I preferred to include the modified AjaxControlToolkit as a project in the solution.

But the rebuild using the Microsoft Visual Studio 2008 caused the following warning messages and prevent the solution from a success build.

C:\BSH\FSB\FSBWeb\App_Code\FSBFunctions.vb(808,0): error BC32206: Indirect reference is being made to assembly System.Web.Extensions version 3.5.0.0, which contains 'AjaxControlToolkit.TabContainer'. This Project references a prior version of System.Web.Extensions version 1.0.61025.0. To use 'AjaxControlToolkit.TabContainer', you must replace the reference to System.Web.Extensions with version 3.5.0.0 or higher.

C:\BSH\FSB\FSBWeb\App_Code\FSBFunctions.vb(822,0): error BC32206: Indirect reference is being made to assembly System.Web.Extensions version 3.5.0.0, which contains 'AjaxControlToolkit.TabPanel'. This Project references a prior version of System.Web.Extensions version 1.0.61025.0. To use 'AjaxControlToolkit.TabPanel', you must replace the reference to System.Web.Extensions with version 3.5.0.0 or higher.

I have looked at the references of the AjaxControlToolkit project in the solution by expending the References node.

When I looked at the properties of the System.Web.Extensions.dll by opening the context menu like shown below:

You can see that the referenced dll file path is "C:\Program Files\Reference Assemblies\Microsoft\Framework\v3.5\System.Web.Extensions.dll" which has .NET Framework version "3.5.0.0"
This is not the correct version for the System.Web.Extensions.dll

When I looked at the same details for the references on an other computer that I can build the solution successfully. I see that the referenced System.Web.Extensions.dll assembly is referenced from the location path "C:\Program Files\Microsoft ASP.NET\ASP.NET 2.0 AJAX Extensions\v1.0.61025\".

So I have removed the references System.Web.Extensions.dll and System.Web.Extensions.Design.dll assemblies first. And then added both assemblies from path "C:\Program Files\Microsoft ASP.NET\ASP.NET 2.0 AJAX Extensions\v1.0.61025" by browsing on the Add Reference dialog screen.
After I have rebuild the AjaxControlToolkit project and the solution, the error were resolved and build was successful.