We use VMWare Player in class to demonstrate various versions of Windows as need arises. Since we teach both Linux and Windows, and Windowx 7 and Windows XP are still used in industry, this allows us to manage our mission without needing to create special partitions for each possible configuration.
However, whenever Linux upgrades, the VMWare becomes unusable for a month or two until VMWare catches up. To run, the VMWare Player must be compiled with the current Linux headers — and recomiled every time Linux is upgraded or updated. After teh upgrade to Ubuntu Oscelot 11.10 there was another glitch: no headers: this stops the whole process cold.
If you upgraded to 11.10 and lost your headers, run the command line
sudo apt-get install build-essential linux-headers-$(uname -r)
to install them again. Then download the current (free) version of VMWare Player from VMWare.com and run that downloaded file as a script. You may need to chmod to make it executable.