Windows Server 2012 R2 go Stuck after guest additions

[BlackChart]

I'm trying to install and configure a Windows Server 2012 R2 Datacenter edition under Virtualbox 4.3.30.

After installing guest additions I can no longer boot the guest - it just go stuck.
I see some R0 Assertation failures in the log, but nothing more that gives me a clue.

Log attached.

[noteirak]

VirtualBox VM 4.3.30 r101610 linux.amd64 (Jul 10 2015 14:01:34) release log
00:00:00.066814 Installed Extension Packs:
00:00:00.066841 Oracle VM VirtualBox Extension Pack (Version: 4.3.31 r101913; VRDE Module: VBoxVRDP)

Try be installing the release extension pack and not the test one.

[BlackChart]

Same scenario. Installed the test to Be able to use RDP from a Win10 client.