Question: Is it possible to host a .NET 4 application under a .NET 2 site?

For several reasons we have to run the main site on .NET 3.5, but there is an application written in entity framework 4, which hosted under the same domain/port. 

When I try to add an application under the site (using a different .net 4.0 application pool), i get an error stating duplicate content in web.config. I have searched the net for fixes, but none of them seems to be working for me.

I am running a Windows Server 2008 R2 with IIS7.5

Any help would be appreciated.

Answer: 
It is possible to fix, if you carefully read Microsoft's document,

<http://msdn.microsoft.com/en-us/library/a99txfy5.aspx>

and

<http://www.asp.net/whitepapers/aspnet4/breaking-changes#0.1__Toc256770150>
No, that's not possible. An assembly compiled against .NET 4.0 must be run inside CLR 4.0. It is possible the other way around: run an assembly compiled against .NET 2.0 inside CLR 4.0.