virtualbox.org

Hardware: i5-2320 CPU, 2 GB RAM, GT 520 graphics. VT-x is enabled.
Host OS: Xubuntu 15.04 64-bit.
Guest OS: Windows Server 2012 R2 Datacenter 64-bit (Full GUI).
Both OSes have been recently installed and are essentially still clean installs.
VirtualBox: 4.3.26_Ubuntu r98988. Extension pack and VNC pack are installed (same versions).
EFI, VT-x, Nested Paging, 2D and 3D acceleration, and PAE/NX are enabled for the guest.
The guest also has 64 MB of VRAM and 768 MB of system RAM assigned.

When I install the guest additions, it asks me to reboot. However, it never finishes, and freezes the entire host OS at the last step. When I restart and turn on the VM, as soon as I login, the host OS freezes. http://i.imgur.com/IPk8uzG.png is what I see when it freezes up (I used a remote desktop software to be able to take a screenshot of it when it froze).

VBox.log: http://pastebin.com/QAwW35ip
VBox1.log: http://pastebin.com/BwRp5NW4
The rest are attachments. I would've made these two attachments, but they're over the maximum allowed file size of 128 KB.

aaronfranke wrote: The rest are attachments. I would've made these two attachments, but they're over the maximum allowed file size of 128 KB.

I believe that's why people compress them first.

What happens if you disable 3D support for this VM?

Frank Mehnert wrote:What happens if you disable 3D support for this VM?

Now it's working fine! Can someone explain why denying the VM something causes it to work, and why it only happens with guest additions?

I'm not sure why that would be a surprise. 3D support is an experimental feature. Denying access to something means you can't trip over it.