[Webtest] scriptStep Classpath problem

[Thomas Colin de Verdière]

Hello
i have a problem to use scriptStep. That's the same problem referenced 
as the issue :
http://webtest-community.canoo.com/jira/browse/WT-179

ERROR (org.apache.bsf.BSFManager) - Exception :
java.lang.ClassNotFoundException: 
org.apache.bsf.engines.javascript.JavaScriptEngine
at java.net.URLClassLoader$1.run(URLClassLoader.java:200)

but i don't know were to seek first to solve this problem. Is this an 
Ant problem or WebTest problem ?

Thank you

Thomas