While playing with IIS 7 I accidental destroyed my IIS (XML) settings file. To fix this problem I copied the .XML from a colleague PC to mine. After this my IIS started giving a strange error:

HTTP Error 404.17 - Not Found - The requested content appears to be script and will not be served by the static file handler.

After a quick search I found out that I copied the .XML from a 32 bit PC to my 64 bit Vista and that all my Application Pools where now running on 64-bit. So my application stopped working because it's 32 bit.

To fix this problem go to IIS, right click your Application Pool and set the Enable 32-bit Applications to true.

If you run your website on IIS7 you can run into the following HTTP errors: 500.22, 500.23

If you don't want to change your web.config and still want to run the website on IIS7 you have to change the Application Pool of your Website.

Open IIS, go to your Application Pools, find your Application Pool and double click the Managed PipeLine Mode.

Set the Manage Pipeline mode from Integrated to Classic.

Set IIS7 Application Pool Defaults
You can also set the Manage pipeline mode in the Application Pool Defaults. You can do this in IIS7 by clicking on Set Application Pool Defaults.

And then change the Managed Pipline Mode to Classic.

The other way is changing your web.config to work with IIS7. You can get more information about this by reading this post.