Same error here. I’m running a CHR 6.41.4 on Windows Hyper-V 2008R2, when trying to upgrade to latest version 6.42.2 and reboot I get:
Loading system with initrd
ERROR: could not find disk!
Please attach it somewhere else.
Tryed upgrade to 6.42 and 6.43rc17 with same error.
I downloaded new chr-6.42.2.vhdx (convert to vhd) and runsit on a new virtual machine, same error.
I tried same vhd on a VirtualBox machine and it works, seems to be loading others storage drivers:
VirtualBox on 6.42
i]# IRQ USERS
4 14 ide0
5 15 ide1[/i]
HyperV 2008R2 and VirtualBox on 6.41
# IRQ USERS
4 14 ata_piix
5 15 ata_piix
Any workaround? CHR dropped support to 2008R2 on purpose?
Contact support and inform them.
A year or two ago I had an issue where the router should boot and you could login via console but everything timed out. They told me that it should work and they had no issues.
After a while they told me the tested on Windows 10 Hyper-V which is = Server 2016 and I run 2012 R2 Hyper-V which is Windows 8.1. So when they tested on correct Hyper-V version everything worked again. So my guess is that they do not test Hyper-V on Windows 2008 R2.
If your server can handle it you should which to newer version. Hyper-V is free if you download just the hypervision Windows Server version. There is no GUI but otherwise it works great.
I’ll contact support, we’ll see what they say, thanks
I Tried 6.42.3 and 6.43rc19, same result
New RC release. Test if this will work for you. My guess is they have fixed an issue.
*) chr - fixed boot on hosts older than Windows Server 2012 when running CHR on Hyper-V
But you might already know this as you might be the one who reported this issue in the first place 
Seems to work now! running routeros-x86-6.43rc23 and dude-6.43rc23
Thanks!