Background
Our server is running Windows Server 2008 R2 SP1 with IIS 7.5.
Yesterday, we updated a site from DNN 7.3.1 to 7.4. Ever since then, links will only work with a .aspx on the end of them. For example, http://www.example.com/Download.aspx works, but http://www.example.com/Download will return a 404 error. This has only happened since updating to 7.4. The extensions URLs worked before the update.
Googling took me to this wiki page which recommended changing the urlFormat of the DNNFriendlyUrl entry in web.config from human friendly to advanced, i.e.
<add name="DNNFriendlyUrl" type="DotNetNuke.Services.Url.FriendlyUrl.DNNFriendlyUrlProvider, DotNetNuke.HttpModules" includePageName="true" regexMatch="[^a-zA-Z0-9 _-]" urlFormat="advanced" />
Problem
Making this change as recommended causes an infinite redirect loop:
This happens on any URL we try to load, with or without the .aspx extension.
What I've tried
The wiki page linked above noted that a prerequisite to activating advanced URL management was the installation of hotfix 980368, which would not install on our server. A Server Fault question suggests this is because we have Service Pack 1 installed.