"File not found"
while your program is really there and it is not missing, then your problem might be that you are trying to run a 32-bit executable on a 64-bit computer.
The solution is to install the ia32-libs package for backwards 32bit compatibility. Run:
1) dpkg -s ia32-libs ; to check whether the ia32-libs package is installed or not
2) open "Ubuntu Software Center", search for "ia32-libs", click "install"