Can you trying determining the path from where ArrayStack class is getting loaded You can either use method as in [1] or something like
org.apache.jackrabbit.commons.AbstractRepository.getResource("/org/apache/commons/collections/ArrayStack.class")
org.apache.commons.collections.BeanMap.getResource("/org/apache/commons/collections/ArrayStack.class")
To see from where the class is getting pickedup
Chetan Mehrotra
[1] http://snippets.dzone.com/posts/show/3719
