ChetOS.net

In II6, and in II7 "classic mode", httpModules are defined under:

<configuration>
    <system.web>
        <httpModules>

However, in II7 "integrated mode" (the default mode), they are defined under:

<configuration>
    <system.webServer>
        <modules>

Now, remember that Vista, Windows 2008, and Windows 7 come with IIS7, while XP and Windows 2003 come with IIS6.  This means that if you are developing a website on a machine with one version, and you deploy it to a machine with a different version, you will get errors saying that the module was not specified in the web.config file.

Best practice is to always define the module in both places so it will continue to work no matter what version of IIS is being used.

Some modules are nice enough to indicate, in an exception, exactly what you need to specify in the web.config file.  However, the particular module that I was working on was older and didn't remind you to specify the module in the IIS7-specific section.