ECCE 6.3. Install/Java Problem
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Gets Around
1:38:55 PM PDT - Thu, May 3rd 2012
Here's another message board thread with the same error message starting ActiveMQ:
http://activemq.2283324.n4.nabble.com/Failed-to-execute-main-task-Reason-java-lang-NoClass...
The solution to this was related to updating java, although they are talking about older versions than what you are apparently running.
Gary