Preseed partman-auto expert_recipe not working

I have the following in a preseed file for ubuntu 16.04

# Partitioning
d-i partman-auto/disk string /dev/sda
d-i partman-auto/method string lvm
d-i partman-auto/purge_lvm_from_device boolean true
d-i partman/choose_partition select finish
d-i partman-partitioning/confirm_write_new_label boolean true
d-i partman-lvm/device_remove_lvm boolean true
d-i partman-lvm/confirm boolean true
d-i partman-lvm/confirm_nooverwrite boolean true
d-i partman-md/device_remove_md boolean true
d-i partman-md/confirm boolean true
d-i partman/confirm_nooverwrite boolean true
d-i partman/confirm boolean true

d-i partman-auto/choose_recipe select bios-boot-root-swap
d-i partman-auto/expert_recipe string            \
    bios-boot-root-swap ::                       \
        512 10 512 ext4 \
            $primary{ } $bootable{ } \
            method{ format } format{ } \
            use_filesystem{ } filesystem{ ext4 } \
            mountpoint{ /boot } . \
        6144 20 -1 ext4 \
            $defaultignore{ } \
            $primary{ } \
            method{ lvm } \
            device{ /dev/sda } \
            vg_name{ vg00 } . \
        1024 110 50% linux-swap \
            $lvmok{ } \
            in_vg{ vg00 } lv_name{ lv_swap } \
            method{ swap } format{ } . \
        5120 120 -1 ext4 \
            $lvmok{ } \
            in_vg{ vg00 } lv_name{ lv_root } \
            method{ format } format{ } \
            use_filesystem{ } filesystem{ ext4 } \
            mountpoint{ / } .

I put this together based on what I could find online. The ubuntu documentation for doing this is woefully inadequate!

Basically, what I want to do is set up to automatically install Ubuntu 16.04 desktop on BIOS based PCs. I've been testing this on a VirtualBox VM at this time. I have a single disk in the VM. I've tried with 10GB and 20GB virtual disks. I want a /boot partition that is 512MB in size. I want another primary partition to be the rest of the disk. I want to use that partition as a physical volume for a LVM volume group named vg00. Within that volume group, I want a swap partition that is at least 1GB in size, but no greater than 50% of my total RAM, which is 4GB in my VM. I want a second logical volume for the root partition (i.e. /).

The above appears to work to get the OS installed. However, when the install is done, the VM fails to boot. It gives me the VirtualBox VM BIOS firmware screen. It then blanks out.

I have no problems with setting up something similar with just plain partitions. That works just fine. When I try to switch to using LVM, it took over 2 days to get the preseed file to a point where the OS installs. Now though, I do not know how to proceed.

Any help figuring out what is wrong with my preseed would be greatly appreciated.

Thank you