Alien arena 7.51 is not working at all in either Unity or GNOME Shell. I am using a Thinkpad T510 with nvidia NVS 3100 discrete graphics. When I press the icon nothing happens. Alien arena worked in Ubuntu 11.04 64 bit on the same laptop.
Maybe you can try:
rm -v ~/.config/alien-arena
mkdir -p ~/.config/alien-arena
Regards (source: http://ubuntuforums.org/showthread.php?t=1882171)