It would help a lot if you would show the error you get. Also I recommen d to make a local copy of the system macro in your user settings directory and change this copy, otherwise your modifications would be overwritten when jEdit is reinstalled or upgraded.

Which version of jEdit you are using. You should use 4.3pre12 or 4.3pre13. jEdit betas are actually very stable.

RunScript.bsh needs also Console plugin to be installed.
I looked and at least 4.3pre13 includes already ruby mode so running ruby scripts should work out of the box and you do not need to change the macro.

Thanks to Beanshell there are a lot of other ways you could get ruby code to evaluate.