There have been some issues with the installation of older GAMS distributions on Ubuntu Linux 64 bit (Linux ubuntu64 2.6.22-14-server). The main issue issue is that by default only 64bit programs will work there.
Old GAMS installation scripts still relied on some 32bit programs (unzip) and thus did not work on a pure 64bit system. Also some solvers were still 32 bit based and would not have worked either.
To install an old GAMS in such an environment, one would have needed to install the missing 32 bit libraries.
These are part of the Linux Standard Base (see http://www.linux-foundation.org/en/LSB) and can be installed simply by:
sudo apt-get install lsb-core sudo apt-get install ia32-libs
gamsunpack fails, you will also have to install the tcsh package.
With a current GAMS system, these steps should not be necessary anymore.