.NET using wrong 2.0 machine.config instead of 4.0

Question

I have a .NET web application install on IIS 7.0 Windows Server 2008 R1. I have installed .NET 4.0 on the server and configured an app pool for 4.0 and integrated pipeline. For some reason I am getting the following error:

(500.19) The configuration section 'system.web.extensions' cannot be read because
  it is missing a section declaration.

It appears that it is using the wrong machine.config file from V2.0 .NET rather than the machine.config file which has defined the system.web.extensions config section. I proved this by replacing the machine.config file in the V2.0 framework with the one from the V4.0 framework and the web application no longer throws the 500.19 error. I have tried to uninstall and reinstall .NET 4.0 as well as running aspnet_regiis -i.

Any thoughts on why it would be trying to using the 2.0 machine.config?

Answer 1

Not sure, that it's realy reason/solution, but last thing I've try it is (in IIS Manager):

1. Navigate to server in right panel (root node)
2. In the features list open "ISAPI and CGI Restrictions"
3. There is 2 items with descriptions ASP.NET v4.0.30319 with restrictions set to Deny
4. Set restrictions value to Allowed

This is last thing i've tried before issue is gone.