Hello David,
look at your SAP Logon options to find the saplogon.ini file, where the connections are stored.
Is it possible that you install the new SAP GUI for Windows with another user? This could be a reason why you can't edit the file. Set the Connection to your saplogon.ini file and all should be run well.
As far as I know the SAP GUI for Windows installation program doesn't install a standard saplogon.ini.
Cheers
Stefan