Dual Booting 32 bit and 64 bit Linux not working

[Robert Steinmetz,,,]

I have a computer which has 32 bit Ubuntu 18.04 on it. Ubuntu has been 
updated to successive LTS versions and is currently 18.04.6 32 bit. I 
need to move to 64 bit so I installed 64 bit 18.04 along side the 
original 32 bit version. I intended to transfer the configuration from 
32 bit to 64 bit verify they both worked then remove the 32 bit. I had 
both versions running at one time, however something happened and the 64 
bit install won't start, it says it is unable to mount the root 
partition and panics.

The computer has 4 hard drives configured as two RAID 1 arrays with LVM2 
on the each with three volumes.

When I boot into the GRUB menu I see a default entry for Ubuntu (the 32 
bit default) and two kernels. I also see a listing for Ubuntu 18.04 on 
dev/mapper/system-root which is the 64 bit install.

I can select any of the items in the grub menu and I can open the settings.
I can boot into the 32 bit kernel and I have all of the lvs mounted in 
/etc/fstab. I can go into the files and see everything in them. As far 
as I can tell they look fine.
But when I try to boot the 64 bit kernel I get an error "unable to mount 
root fs on unknown-block (0,0)" then a kernel panic.

--

Robert Steinmetz AIA
Principal
Steinmetz & Associates

New Orleans & Atlanta