ASP.NET MVC2/MVC3 - EnableExtensionlessUrls registry key disappeared?

Windows Server 2003 (IIS6), .NET 4.0

I recently upgraded one of my sites from MVC2/.NET 3.5/ASP.NET 2.0.* to MVC3 and .NET 4. Since running v4 under IIS6 causes all requests to have /eurl.axd?{000000-.....} appended to the request, I had to add the EnableExtensionlessUrls registry key (as described in this article).

This all works fine, however, this morning I got a few emails complaining that parts of the site weren't working. This turned out to be due to the fact that the EnableExtensionlessUrls registry key disappeared. Further investigation revealed that this was the case on all three servers (dev,staging,production).开发者_运维技巧

The only thing I've done recently is install MVC3. Is it possible that the installer removed this key? Any other suggestions?

Looks like this was the result of a series of OS updates/patches.