After installing the 64bit version of Ubuntu, I like many others found that any 32bit virtual machines would no longer play. Trawling through the forums found a fix. Ubuntu 64bit does not install some of the 32bit libraries needed to run the virtual machines. This can be corrected by typing 'sudo apt-get install ia32-libs' in your favorite command shell. Once installed the virtual machines will now run correctly. No reboot or log out needed. Many thanks to the many forums posters on Ubuntu for this solution.