The Ubuntu packages have been republished to fix the non-valid version
However, some people reported that the menu bar disappeared on Ubuntu 11.04.
Meanwhile we fixed this problem, there are some ways to go round this
. install Unity 
. with Classic (Gnome), launch amaya like this : UBUNTU_MENUPROXY= amaya
. without using the terminal, in the file
/usr/share/applications/amaya.desktop, change the line:
[[ Exec=amaya %u ]] with [[ Exec=sh -c 'UBUNTU_MENUPROXY= amaya %u' ]]