User.Identity.Name returns ""

I've been asked to make a modification to a web app that was written in VS2008.  It works fine in production.  Trying to debug it on my machine running VS2013 and I'm finding that User.Identity.Name is returning a zero length string.  Everything I've read so far says to deny "?".  That's fine if I want to deny myself.  It doesn't explain why User.Identity.Name might be returning a zero length string.  Below is the Web.Config.  I'm hoping someone can tell me why User.Identity.Name is returning a zero length string in Debug mode.
Thanks
<?xml version="1.0"?> <configuration> <appSettings/> <connectionStrings> <!-- Removed for this post --> </connectionStrings> <system.web> <authentication mode="Windows"/> <sessionState mode="InProc" timeout="5" cookieName="ETSNotes" ...