virtualbox.org

What if I reduce the number of cores to 2 and remove the extPack ?

That would be a start but probably not fix the real issue. See my conclusion above.

And drive Z: is where I keep all my VM's.

I kind of figured that part out but it still leaves me with the same question of just what the z: drive is. External drive, network drive, Etc..

Z is a internal HDD.

I have found a workaround for this problem.
Make a Host-only adapter on the guest and then SCP files into it by using something like Git bash from the host.
Not really elegant but is a good workaround if only file transfers are required to and from the guest.