Can't reliably foot 14.04 in a virtualbox vm

I've run ubuntu in a virtualbox vm hosted on windows for years now and never had the slightest problem.

Until I tried 14.04. Like everywhere else I've tried 14.04 (server, native on a laptop) it has been a complete disaster.

4 out of 5 times it'll lock up -- purple screen of death? Only recourse is a hard reset.
When it does finally make it to starting X, there will be a half dozen "system program problem detected" against a black background.
Clicking on "report" is the same as clicking on "cancel". Trying to report the problem does nothing that I can see.
About 60% of the time, clicking cancel on the dialogs does nothing and the system stays in a locked up state; again a hard reset is the only recourse.

When it finally gets around to displaying the desktop, that process often can take the better part of 5 minutes. Or come up in 10 seconds. I never know.

Is there any way to diagnose these lockups? I tire of needing to lose a half hour of my time every time I try to bring up ubuntu 14.04 within virtualbox.
Virtualbox version: 4.3.26
Ubuntu uname -a: Linux afelson-VirtualBox 3.16.0-33-generic #44~14.04.1-Ubuntu SMP Fri Mar 13 10:33:29 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux