I have been running Ubuntu 13.04 successfully on a MacBook Pro in a virtual machine in Parallels Desktop 9.

Today (2013-10-17) after applying today's Ubuntu update, which included updates to X Windows, my Ubuntu 13.04 virtual machine launches, the launcher comes up, but the screen background is solid black, rather than the shaded orange colour of the default desktop background (and my desktop icons are "hidden behind this blackness", as well). I can launch applications from the launcher, and there is a very brief white flash on the screen, and then it returns to black. It's as if there is a "black blanket" covering the entire screen, so there is no way to interact with any application windows using the keyboard or mouse. The icons of the launcher are responsive to the mouse, so I can right-click and quit any application I have launched. But the rest of the screen is non-responsive to keyboard or mouse.

This same behaviour happens with two different versions of Parallels Tools, so I am quite sure this is not a Parallels problem per se, although I could believe that it could be a paroblem with the interface between Parallels and this new updated X Windows code.

Could anyone tell me what has happened, and how I might be able to fix this problem, so I can continue to use my Ubuntu 13.04 virtual machine?

(I do have the option of reverting to a previous version of my virtual machine from before this update, but if possible I would prefer to keep my version of Ubuntu 13.04 up to date with the latest updates.)

Thanks, Bob