Java for AMD64 Linux has one issue for running Rjb. The Zip shared object that came with JRE causes 'unknown exception'.

The workaround is to put LD_PRELOAD environment variable before invoking the script.

For example to run Rails sciprt/server as:
% LD_PRELOAD=/opt/jdk1.5.0_09/jre/lib/amd64/libzip.so script/server

The pathname '/opt/jdk1.5.0_09/jre/lib/amd64' is varied according to the installation process.