During the creation of a SharePoint 2013 Enterprise server to investigate PowerPivot I ran into an odd issue during the SQL Server 2012 SP1 configuration.  Following the instructions here, I found that at the Instance Configuration step, the named instance screen was blank and un-editable, but installation failed to continue because I got the error “The Instance name is required but is missing.”  Below is how the screen looked.

The fix was easy, right-click on the SQL Server setup.exe file and choose Run as Administrator.  Oddly, I had to do this even that User Account Control was disabled on the server.  The named instance was then correctly populated as shown below.