Folks, a couple of weeks ago, after upgrading to Visual Studio 2017, I asked if anyone could guess why debugging any web app produced a "not found" popup for the start page. I finally discovered it was caused by Edge being the default browser instead of Internet Explorer. By sheer luck, or some mental burp I right-clicked the start page node in the solution explorer and clicked "Browse With ...", and there I noticed Edge was the default.
For weeks I suspected file permissions, IIS, pool attributes, account privileges, marriage equality, anything ... there was absolutely no clue to be found in any messages or web searches. It turns out the cause was in a little-used context menu right under my nose all the time. *Greg K*
