Lately, I needed to set up VirtualBox on some server I use to ssh into, and I wanted to use the GUI for initial setup. I did this previously, without any problems – ssh -X, then just start the GUI.
Not so with VirtualBox 5, the only message I got was libGL error: failed to load driver: swrast.
Turns out that the VirtualBox 5 GUI uses OpenGL, while previous versions didn’t, and there seem to be some issues whether that should be rendered locally or remotely.
Finally I found a solution in a 20 year old discussion: https://groups.google.com/forum/#!msg/comp.security.ssh/DXHF6hGznYI/15zYRY4L5pYJ is still valid.