Cannot install guest Additions on 8.1 Enterprise guest

[PSZ]

I have created a new VM with Windows 8.1 Enterprise 64-bits as a guest OS (Windows 7 Ultimate 64- bits as host). Whenever I try to install the guest additions, as soon as it gets to the video WDDM driver, the VM's screen goes black and all HDD/DVD activity stops. The network icon shows a little intermittent activity for a minute or so, then falls to zero activity. However, the CPU used by Virtual Box on the host is constant at 50%. My only recourse it to force the VM shut.

This behavior started 2 VB versions back (4.3.10) and hasn't changed with the latest (4.3.16). I have had no such difficulty with an 8.1 Pro VM.

Any hints, please?

[phietone]

I have the same issue but on guest additions 4.3.20 with exactly the same setup (VB: Win 8.1, Host: Win 7 enterprise 64 bit)
Anybody has any ideas?