Your error is clear. While you are iterating over listAcumulador with ListIterator acumuladorIt, you are applying add and remove methods to listAcumulador -- this is enough to cause the exception.
I don't understand your code so I can't suggest specific code, but among your options is to (1) use *ListIterator's* add and remove methods, or (2) make a copy of your list and iterator over the copy, but change the original list (be careful if you choose to do this!).
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