Error while doing a build

I am getting following error when doing a build (I am doing a build on VS 2010 Express)

Error  1  Could not load type 'System.Data.Entity.Design.AspNet.EntityDesignerBuildProvider'.  C:\Windows\Microsoft.NET\Framework\v4.0.30319\Config\web.config  129  


Any ideas, why I may be getting this error. This a first build I am doing.

Any one out there with an idea on why this exception

It seems like an error in .NET. Can you build other projects?

Hard to give a solution but I would redownload/install the .net 4.0. Maybe search in the microsoft knowledgebase.