ASP.Net 404 Ingestion Error

So, I configured the rule in IIS7 to redirect to a specific page with a 404 error.

This works fine while I type in the urls, for example:

www.abc.com/Test/

However, as soon as I try to access a file that does not exist

www.abc.com/Test/Test.aspx

I get an ASP.Net error message:

Server error in application "/".

Resource is not found.

How can I keep ASP.Net from swallowing 404 errors and overriding my settings in IIS7?

EDIT: Here is my web.config file. IIS added the system.webServer file to me.

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
    <system.web>
        <customErrors mode="Off"/>
    </system.web>
    <system.webServer>
        <httpErrors>
            <remove statusCode="403" subStatusCode="-1" />
            <remove statusCode="404" subStatusCode="-1" />
            <error statusCode="404" prefixLanguageFilePath="" path="/redir.aspx" responseMode="ExecuteURL" />
            <error statusCode="403" prefixLanguageFilePath="" path="/redir.aspx" responseMode="ExecuteURL" />
        </httpErrors>
    </system.webServer>
</configuration>