Exactly same issue as the MAIN POST But the solutions given in that post didn't solve the issue.
I was working with VirtualBox 4.3.10 in Windows 8 with Ubuntu 14.04 as Guest. Once I upgraded to Virtualbox 4.3.12, then suddenly launcher and taskbar is missing. No Terminal working.
Please note, I have tried the options in the MAIN post. So this seems to be another kind of issue.