Sorry if I missed this in the thread somewhere, but is it only me who has trouble starting up (get forbidden sign) my macOS Sierra installation that I use with my Mac Pro with a non-EFI NVIDIA card on a "normal" Mac?
Previously I have been taking out the drive from the Mac Pro to start up from it on a MacBook Pro to install the OS update and apply the new Web Driver from NVIDIA. This is to avoid the hassle of having too take out the non-EFI graphics card, put in the EFI one, do the OS update and install the new Web Driver, take out the EFI graphics card and then finally put the non-EFI card in again.
Unfortunately it seems the latter process is what I have to go through now... Am I the only one having this problem , or is this the way it is (for whatever reason) with Sierra?