Actions in RuleFlow are interpreted at runtime using MVEL. This error seems to indicate that there is a problem in the syntax of your MVEL expression. However, looking at your example, I do not see any problem, System.out.println("Your text here"); as action property should work (I just tested it with the 4.0.1 release). Could you open a JIRA and provide a self-contained test that shows the problem?

That said, we still need to add syntax checking for actions during ruleflow validation, to ensure that this error is encountered when checking the ruleflow (at compile time) and not during execution.