Feb 25, 2014 12:25 AM|Starain chen - MSFT|LINK
Based on this link
http://www.asp.net/whitepapers/aspnet4/breaking-changes , it said that:
Web servers that run SharePoint have a Web.config file that is deployed at the root of a SharePoint Web site (for example, c:\inetpub\wwwroot\web.config for Default Web Site). In this Web.config file, SharePoint sets a custom partial-trust level named WSS_Minimal.
If you try to run an ASP.NET 4 Web site that is deployed as a child of this type of SharePoint Web site, you will see the following error:
Could not find permission set named 'ASP.Net'.
This error occurs because the ASP.NET 4 code access security (CAS) infrastructure looks for a permission set named ASP.Net. However, the partial trust configuration file that is referenced by WSS_Minimal does not contain any permission sets with that name.
Currently there is not a version of SharePoint available that is compatible with ASP.NET. As a result, you should not attempt to run an ASP.NET 4 Web site as a child site underneath SharePoint Web sites.
There is a related thread that may benefit you:
but I will give the sharepoint forum a go.
Please post the link here which will be benefit to others who has the similar issue.