So here's the situation.
I have 2.0 working fine on a 16G microSD card. I install 2.1.2 on another 16GB microSD card and the system does not recognize it when I do Ctrl-U. However, IF i put the sd card in a usb adapter (or just use a flash usb stick) and do the ctrl-u it works fine.

If I put back in the 2.0 microSD card and it also works fine.