I'm experimenting with installing Yosemite on a new PCIe SSD I've installed in my Mac Pro 5,1 6 core 3.3ghz. My main system is still Mountain Lion and it works beautifully - is stable, fast - but I wanted to see what apps I could migrate to Yosemite on the new drive with a view finally to upgrading. When I switch systems and Yosemite boots on the new drive, I'm presented with my admin name and asked for my password and I enter this successfully but then when I go to change settings in preferences and elsewhere and need to unlock, it asks for Administrator's Name and Password. There's nothing in the Admin space so I naturally put in the Admin name (the same one I'm presented with at the boot up) and then the same password but it won't accept these. What is going on???? To return to my old Mountain Lion system I then have to restart and press N to select the old drive.