Can't run encog on Mac

After downloading encog workbench I have not being able to run the jar file, either by double-clicking on it, or typing "java -jar encog-workbench-3.0.0-executable.jar" (the README file says "java -jar encog-workbench-3.0.0-SNAPSHOT-executable" but there is no such file). The same thing happens with newer versions. Is there anything else I have to do before that? I have java version "1.5.0_30" (mac) Thnx.