Here is the answer that has worked for me, and it is a combination of some of the above answers.
First install / uninstall / reinstall the following packages:
Install-Package Microsoft.AspNet.Web.Optimization Update-Package WebGrease Uninstall-Package Microsoft.AspNet.Web.Optimization Uninstall-Package WebGrease Install-Package Microsoft.AspNet.Web.Optimization Update-Package WebGrease
Then make a copy of the contents of ~/Views/Shared/_Layout.cshtml
delete the _Layout.cshtml file, recreate it and paste the contents back in.
this is the final fix that has worked for me.