[SOLVED] Expected data of type IOObject

I have created a new filter operator and added it inside the ProcessDocument operator, after Tokenize operator.

When I try to run the process, the following error occurs.
Process Failed
Wrong data of type of Document was delivered at port 'document'
Expected data of type IOObject

The xml of the ProcessDocument is

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<process version="5.3.000">
  <context>
    <input/>
    <output/>
    <macros/>
  </context>
  <operator activated="true" class="process" compatibility="5.3.000" expanded="true" name="Process">
    <process expanded="true" height="-20" width="-50">
      <operator activated="true" class="text:read_document" compatibility="5.3.002" expanded="true" height="60" name="Read Document" width="90" x="112" y="75">
        <parameter key="file" value="D:\\RapidMiner\DataSets-DataMiningforthe Masses\Text.txt"/>
        <parameter key="encoding" value="UTF-8"/>
      </operator>
      <operator activated="true" class="text:process_documents" compatibility="5.3.002" expanded="true" height="94" name="Process Documents" width="90" x="380" y="75">
        <process expanded="true" height="228" width="1049">
          <operator activated="true" class="text:tokenize" compatibility="5.3.002" expanded="true" height="60" name="Tokenize" width="90" x="45" y="30"/>
          <operator activated="true" class="operator:filter_stopword_nlp" compatibility="1.0.000" expanded="true" height="60" name="Filter Stopwords (NLP)" width="90" x="179" y="30"/>
          <connect from_port="document" to_op="Tokenize" to_port="document"/>
          <connect from_op="Tokenize" from_port="document" to_op="Filter Stopwords (NLP)" to_port="document"/>
          <connect from_op="Filter Stopwords (NLP)" from_port="document" to_port="document 1"/>
          <portSpacing port="source_document" spacing="0"/>
          <portSpacing port="sink_document 1" spacing="0"/>
          <portSpacing port="sink_document 2" spacing="0"/>
        </process>
      </operator>
      <connect from_op="Read Document" from_port="output" to_op="Process Documents" to_port="documents 1"/>
      <connect from_op="Process Documents" from_port="example set" to_port="result 1"/>
      <portSpacing port="source_input 1" spacing="0"/>
      <portSpacing port="sink_result 1" spacing="0"/>
      <portSpacing port="sink_result 2" spacing="0"/>
    </process>
  </operator>
</process>

Any idea what can be wrong?