You initially tried to install to /dev/sda, which failed. Due to another known bug, after the first try fails, all subsequent attempts will also fail, so please try to install again and be sure to use /dev/sdb the first time.
You initially tried to install to /dev/sda, which failed. Due to another known bug, after the first try fails, all subsequent attempts will also fail, so please try to install again and be sure to use /dev/sdb the first time.