[Webtest] scriptStep error invoking inline javascript

[Caleandro]

Hi all,

I'm using Canoo Wetbtest rel 2.0 build 1393 from a lot of time, but for 
the very first time I try the scriptStep step. I try this very basic 
example:
...
<steps>
<group>
<scriptStep description="Lo script effettua la somma di due parmetri 
passati in input" language="javascript">
    somma = 0;
    addendo1 = 10;
    addendo2 = 20;
    somma = addendo1 + addendo2;
    step.setWebTestProperty('sommaCalcolata', somma);
</scriptStep>
<storeProperty description="uso il valore calcolato" 
property="risultato" value="#{somma}"/>
</group>
</steps>
...
And I got the error:

- <#> <error 
exception="*com.canoo.webtest.engine.StepExecutionException*" 
message="*Error invoking script: java.lang.ClassNotFoundException: 
org.apache.bsf.engines.javascript.JavaScriptEngine*">
- <#> <![CDATA[

com.canoo.webtest.engine.StepExecutionException: Error invoking script: java.lang.ClassNotFoundException: org.apache.bsf.engines.javascript.JavaScriptEngine, Step: ScriptStep at D:\TESTSROOT\SIST\BatchTests\Provascript.xml:25:  with (description="Lo script effettua la somma di due parmetri passati in input", language="javascript", script="
	somma = 0;
	addendo1=10;
	addendo2=20;
	somma = addendo1 + addendo2;
	step.setWebTestProperty('sommaCalcolata', somma);
", taskName="scriptStep")
	at com.canoo.webtest.extension.ScriptStep.doExecute(ScriptStep.java:72)
	at com.canoo.webtest.steps.Step.execute(Step.java:132)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
	at java.lang.reflect.Method.invoke(Unknown Source)
	at org.apache.tools.ant.dispatch.DispatchUtils.execute(DispatchUtils.java:105)
	at org.apache.tools.ant.Task.perform(Task.java:348)

	... and so on...

Although I looked at the mailing list archive
messages for any similar question and  
I found some threads,
I'm not able to solve this problem (not even whith the help of 
link 
[ http://webtest-community.canoo.com/jira/browse/WT-179?page=all ]).
Can anyone give me further suggestion ?
Thanks in advance,
Vito Caleandro