How to fix "Root element is missing." when doing a Visual Studio (VS) Build?

In my case it was the xxxxxxxxxxxx.vcxproj.user file that was causing the problem; it was blank after a crash. I renamed it and the problem went away.

Make sure any XML file (or any file that would be interpreted as an XML file by visual studio) has a correct XML structure - that is, one root element (with any name, I have use rootElement in my example):

<?xml version="1.0"?> 
<rootElement>
 ...
</rootElement>