Our site has an MVC Rest API. Recently, both the live servers and my development machine stopped accepting DELETE requests, instead returning a 501 Not Implemented response.

On my development machine, which is Windows 7 running IIS7.5, the solution was to add these lines to our Web.config, under system.webServer / handlers:

<remove name="ExtensionlessUrlHandler-Integrated-4.0" />
...
<add name="ExtensionlessUrlHandler-Integrated-4.0" path="*."
     verb="GET,HEAD,POST,DEBUG,PUT,DELETE"
     type="System.Web.Handlers.TransferRequestHandler"
     resourceType="Unspecified" requireAccess="Script"
     preCondition="integratedMode,runtimeVersionv4.0" />

However, this didn't work on any of our live servers; not on Sever 2008 + IIS7.5 and not on Server 2012 + IIS8.

There are no verbs set up in Request Filtering, and WebDAV is not installed on any of our live servers.

The error page gives no further information, and nothing gets recorded in the logs. How do I find out what's preventing DELETE requests from working in iis7.5 and iis8?