Problem with java

I'm making an extension that calls a method of a java class in a jar through
of the Liveconnect. I got to make the call, but it only do the first time, =
the
second the following error is displayed "Error: uncaught exception:
java.lang.reflect.InvocationTargetException", can anyone help me?

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Josu=E9 Leal Moura Dantas