[rules-users] Views???

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Hi,
I 'm new to drools and want to see how the views work(The Agenda
View,The Working Memory View,...). I have created a rule project and a
break point at
workingMemory.fireAllRules()  line in sample class and debugged it as
drools application. After I have selected the working memory variable
as explained in the documentation and opened the Agenda View or the
other views, I got this message:

java.lang.NoClassDefFoundError:
org/eclipse/debug/internal/ui/contexts/provisional/IDebugContextListener
	at java.lang.ClassLoader.defineClass1(Native Method)
	at java.lang.ClassLoader.defineClass(ClassLoader.java:620)  ....

How can I use this views?Did I do something wrong or maybe forget any thing?
thanks in advanced.
M.A