Webapplication unable to run in IIS 7

We have a webapplication, made in ASP.NET 2.

This app runs without problems in IIS 6. When we upload it to an IIS 7 (Windows Server 2008 R2 Datacenter) it runs in IIS, but when we open th开发者_开发百科e site in a browser we get this error:

Server Error
500 - Internal server error.
There is a problem with the resource you are looking for, and it cannot be displayed.

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I would make sure that everything is set correctly in the ASP.NET tab, and also check under the Home Directory tab to make sure that the application has sufficient read/write and execute permissions.

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The problem was that I nedded to add a feature to the server. After I added .NET Framework 3.5.1 Features it worked.