Modifying machine.config in any way causes "Service Unavailable" browser error for SharePoint 2013 site

Question

I need to add some new entries to machine.config on a machine running SharePoint 2013 (server). However, no matter what change I make, after I have saved the file and restarted IIS (both steps are successful), all SharePoint sites return HTTP Error 503 ("Service Unavailable") when an attempt is made to view them in a browser on a client machine.

In Internet Information Services (IIS) Manager, it seems that the entire server becomes unavailable - no application pool or site can be accessed, i.e. trying to click anything returns "Filename:redirection.config / Error: Cannot read configuration file". This error goes away once the original machine.config is restored.

The machine.config file I'm trying to edit is located at: C:\Windows\Microsoft.NET\Framework64\v4.0.30319\Config

Any help on how to resolve this would be appreciated.

Answer 1

Turns out you need to define <sectionGroup> elements in machine.config - I was not aware of that. E.g. if you want to use <Test> key somewhere, you need to add it to the appropriate section elsewhere in machine.config like this: <section name="Test" .../>. More info can be found on MSDN.