"Error occurred while applying DataStreamSimulator"

Dear all, I have little experience in using DataStream Plugin, I met problem to apply it.

The following is  xml of my setup and Error Message Met:
<operator name="Root" class="Process" expanded="yes">
    <operator name="ExampleSource" class="ExampleSource">
        <parameter key="attributes" value="C:\Program Files\Rapid-I\RapidMiner-4.2\streamtest"/>
    </operator>
    <operator name="DataStreamSimulator" class="DataStreamSimulator" expanded="yes">
        <parameter key="data_stream_names" value="a b"/>
        <parameter key="data_stream_relevance" value="a b"/>
        <parameter key="number_of_batches" value="2"/>
        <operator name="BayBoostStream" class="BayBoostStream" breakpoints="before" expanded="yes">
            <parameter key="batch_size" value="3"/>
            <parameter key="keep_example_set" value="true"/>
            <operator name="NaiveBayes" class="NaiveBayes" breakpoints="before">
            </operator>
        </operator>
    </operator>
</operator>

Error Message:
"Process Failed
ClassCastException caught:
com.rapidminer.example.set.RemappedExampleSet cannot be cast to com.rapidminer.example.ConditionedExample"

May I know how I can get correct setup?  Thanks!