VirtualBox fails if guest RAM size 64+GB

There is a problem with Virtualox 5.1.16+ if guest has more than 64GB RAM.
The system (host) has 256GB RAM, but VirtualBox says that only 2.6GB is available (as I was told on VirtualBox forum).
With 5.1.14 everything works great up to 160GB of RAM for guest.
With 5.1.16 and 5.1.18 I cannot start the guest if it's RAM size is set to 64GB or more. Even with 64GB I get guest error: 0x0000005a: ACPI BIOS in the system is not fully compliant with the ACPI specification. (guest is MS Windows 2008 R2 Datacenter)
The only stable run with guest RAM size of 61GB or less.

Does anybody knows what can be the reason of such problem and is anything can be done to fix/workaround the issue?

Log and details can be found here:
(unable to attach a log here)
Host: FreeBSD 10.3 #17.
All ports are up to date.
The system is up to date as well.