I am running an application in IIS 7 as "The Default Web Site" this application is configured to run under an application pool that is running as a .NET 4 application.

As a child application of the Default Web Site I have another ASP.NET application. This application was developed using the .NET 3.5 framework and there can run in an application pool configured to use the .NET 2.0 CLR and Integrated managed pipeline.

The parent application (.net 4.0) runs fine. However I cannot get the child asp.net application to work. I have it configured to use it's own, 2.0 Integrated Application Pool.

The error received is: 500.19 - Internal Server Error

Config source:

111:   </system.web>
112:   <system.web.extensions />
113:   <!-- 

I noticed that the 'Detailed Error Information' points to a problem in the parent application's config file.

**Config Error The configuration section 'system.web.extensions' cannot be read because it is missing a section declaration **

I assume that my issue stems from the fact that my .net 2.0 application is inhering the configuration from it's .net 4. parent. Is there a way to host a .net 2.0 application as a child of a .net 4 application??

  • You are correct that it is a web.config inheritance problem.
    – Mufasa
    Commented Nov 3, 2011 at 20:30

1 Answer 1


You could upgrade your subdomain to use the .Net 4.0 framework.

From what I know, it will be a problem if the parent site uses .Net 4 but your child site uses .Net 2.0. To make it easy, you could run your child site on .Net 4.

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