Today I hade the dubious pleasure of having to work with an old EPiServer 4 site, and having to deploy it to IIS7 on a Windows 2008 Server.

In order to make everything work in EPiServer 4, you need to make sure that all 404-request are redirected to /Util/NotFound.aspx. On my development machine, which runs Windows 7, I accomplished this by adding the following code to web.config:

<system.webServer>
	<httpErrors>
		<remove statusCode="404" subStatusCode="-1" />
		<error statusCode="404" prefixLanguageFilePath="" path="/Util/NotFound.aspx" responseMode=&	quot;ExecuteURL" />
	</httpErrors>
</system.webServer>

Since both Windows 7 and Windows 2008 Server runs IIS7, you would think that this should work on the server as well. But when I ran a particular URL that needed the redirection to NotFound, I only got the following error message:

The page cannot be displayed because an internal server error has occurred.

Nothing else. Nothing in the log files, nothing in the event log. Hmmm.

After fiddling around for a while and trying to figure out what was wrong, I tried going into the Error Pages feature in IIS Manager on the server, and suddenly got the error message saying:

This configuration section cannot be used at this path. This happens when the section is locked at a parent level. Locking is either by default (overrideModeDefault="Deny"), or set explicitly by a location tag with overrideMode="Deny" or the legacy allowOverride="false".

What this basically means is that I can’t use the <httpErrors>-section in web.config, because the machine settings says that I can’t. Now, the settings for IIS7 can be found in the file applicationHost.config, located in C:\Windows\System32\inetsrv\config. A look in this file on both the server and on my machine showed a subtle difference:

<!-- Windows 7 -->
<section name="httpErrors" overrideModeDefault="Allow" />
<!-- Windows 2008 Server -->
<section name="httpErrors" overrideModeDefault="Deny" />

For some reason, the default configuration on Windows 2008 Server doesn’t let you override the httpErrors-configuration in web.config, while the default configuration on Windows 7 does. I’m not saying that either one is more correct that the other, but if it had been the same on both it would have saved me a couple of hours of work today. Sometimes subtle differences can cause a lot of work…