This issue can occur when you are having mutliple jars in the userlib folder, with the same classes like 'XMLInputFactory' in it. For instance:
and also having this class as part of the JDK. Make sure this class is only included once and with the correct version. In this context I believe only including the axiom.jar file will suffice.
This is more a question for stackoverflow than for this forum. You could take a look at this post in stackoverflow: class loader issue
Regards,
Ronald