I was getting some 404 errors while using the FileUpload control. I tested it out on my local machine and  using

<system.web>
        <httpRuntime maxRequestLength="256000"/> <!-- request length is in kilobytes -->
</system.web>

worked fine. But once I moved it onto IIS7 everything started freaking out. Turns out IIS7 look for a different setting:

    <system.webServer>
        <security>
            <requestFiltering><requestLimits maxAllowedContentLength="262144000" /></requestFiltering> <!-- maxAllowedContentLength is in bytes. Defaults to 30,000,000 -->
        </security>
    </system.webServer>

My searches really only directed me to modifying the system.web, so hopefully this will help someone out.