Your boot partition is on a disk using the GPT partitioning scheme but this machine cannot boot using GPT
Following error after telling anaconda to install on pre-existing partitions (with GPT label):
On Partitioning screen, press Ctrl + Alt + F2 to get to a shell prompt.
$ parted /dev/sda -s mklabel msdos
Press Ctrl + Alt + F6 to return to the partitioning screen
