I am on Virtual Box version 4.3.12 (on a Win 7 x64 PC), ALL later versions of VBox due to the new "hardening" or something like that woul not work, crashing on me. I have quite a lot of VMs, windows 2000, XP, 10, and a bunch of Linuxes. I Have NOT tried yet latest VBox (5.0.20 i believe). Stopped trying versions as of 5.012.
What I do is use 4.3.12 and dowload "testing" guest additions the latest.
sparky 4.2 LXQT is working fine in this setup (I use sparky KDE on my notebook)